History of Chittenden County, Vermont, with illustrations and biographical sketches of some of its prominent men and pioneers, Part 3

Author: Rann, W. S. (William S.)
Publication date: 1886
Publisher: Syracuse, N.Y. : D. Mason & Co.
Number of Pages: 1054

USA > Vermont > Chittenden County > History of Chittenden County, Vermont, with illustrations and biographical sketches of some of its prominent men and pioneers > Part 3

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Besides the rocks mentioned there is another series of metamorphic rocks, which have been placed below the Silurian by some geologists, but which ap- pear to belong to the Cambrian. The series includes several kinds of rocks, of which the most common is talcose schist and talcose sandstone. The other rocks are a coarse conglomerate, quartz, limestone and sandstone. The whole

GEOLOGICAL FORMATION OF THE COUNTY.

is called in the Vermont Report "Talcose conglomerate." It is found in Huntington, Hinesburg, Jericho, Milton and Essex. In the Vermont Report the red sandrock is made to be of an age very much later than the Cambrian. Indeed the geologists in charge at that time placed it above the Silurian alto- gether, while we have placed it almost at the bottom of the series ; and here all geologists now agree that it belongs. Thus, during the Cambrian period, where now the red sandrock beds are found the water was in general shallow ; the worm-tracks, ripple-marks and other evidences of shallow water origin, found in the sandstones, show that these are simply the hardened beaches of the pri- mordial sea. Where there are slates and limestones the water was deeper, for these are not formed in shallow water. There does not appear to have been any great disturbance of the strata at the end of this period, and yet there must have been some change, very possibly in the character of the water, for the animals of the Cambrian became extinct at the close of the age, or at any rate before the beginning of the next, when an entirely new group of animals appears. After the Cambrian was finished, all that portion of Vermont now covered by rocks of that age was dry land, and the eastern border of the present Champlain valley was marked out. The ocean about this new land was deeper than that in which the rocks of the first age were formed, and also clearer, and not only a new, but a more extensive fauna inhabited it. Higher and more complex forms now existed, though the life of the globe was no- where at this time of the highest, or very near it. The Canadian period is much less widely represented in this county than the Cambrian. Of the three epochs into which the period is divided, the middle is lacking here, but the lowest, the Calciferous, and the highest, the Chazy, are both found. The Cal- ciferous includes various sorts of rocks from coarse gritty sandstone to lime- stone. It extends along the western side of Vermont from West Haven north to Canada. The southern portion of Lake Champlain has cut a channel for "twenty miles through the rocks of this formation." A portion of the Green Mountains is made of metamorphosed Calciferous rock and a part of a very extensive formation, called in the Vermont Report the Eolian limestone, is of this formation, as shown by Mr. Wing's researches. South of Shoreham rocks of this age are well exposed, but north of this they occur in more or less iso- lated patches. In this county they are found, at least in an unchanged form, only in a few places, and in these only in comparatively small masses. They form the extreme end of Thompson's Point, from which place they run under the lake and reappear on the New York side near Essex. The strata dip slightly to the east. The most common rock of the Calciferous is a hard, gritty limestone, of a gray or drab color ; but there are also sandrocks, some of them very pure, and equally pure limestone is also found. The formation seems to be intermediate between the quartz and sandstones of the Cambrian and the limestones of the Chazy and Trenton. Of the life of the Calciferous,

HISTORY OF CHITTENDEN COUNTY.

so far as this county is concerned, there is very little to be said, for only a few sea-weeds, mollusks, and trilobites, and a few species of each, have been found. In other localities, however, west of us, where the rocks are more fully devel- oped, the fossils are much more abundant. This life is of the same gen- eral sort as that of the Cambrian, but, as has been noticed, it shows progress in number and rank of species. The famous copper mines of Lake Superior are in Calciferous rocks, and at this point they are not less than 10,000 feet thick. Again a change in the life of the globe and in the character of the rocks occurred. The sea bottom sank still more, and deeper and clearer waters allow yet further advance in life. Up to this time all the strata seem to be of shallow water origin, though some of the layers were evidently de- posited in deeper water than others, but yet none of them bear evidence of very deep seas, and it is most probable that the sea bottom was gradually sink- ing, while layer after layer of sand, clay, etc., was laid down, the deposition somewhat nearly keeping pace with the subsidence, until thousands of feet were deposited.

The Chazy epoch brings us to clearer and deeper waters than had before existed, and the progress in life, which the geologist notes as he passes from age to age throughout geological time from the dawn of life on, is strik- ingly manifested as he passes from the Calciferous to the Chazy. There are no plants except sea-weeds, but animals of many sorts grew and flourished ; corals, crinoids, or stone lilies, mollusca in great abundance, and a few trilo- bites, are some of the forms found. In every formation there are more or less unique forms found only in that age, or period, or epoch. These are guides, landmarks which the geologist gladly recognizes, for by them, after they have once been recognized, he determines the age of the rocks containing them. In the Chazy the characteristic fossil, as these are called, above all others, is mac- lurea magna, a large coiled shell, which is the sign of the Chazy. In section this shell is often seen as a narrow spiral line, two or three inches across the outer whorl, and in this form it is common in Burlington on doorsteps or window-sills. The Chazy limestone is usually gray or bluish gray, sometimes light, sometimes dark. It is well shown at McNeil's Point in Charlotte; it forms nearly all of Thompson's Point - all except the little tip of Calciferous mentioned above. From here south it is well developed all along the lake. Its finest outcrop, however, is on Isle La Motte, the southern end of which is almost wholly of this formation. At Fisk's quarry magnificent beds are ex- posed, and they furnish a very compact, durable stone for building purposes. It also occurs near Plattsburgh, and from there north through the town from- which it takes its name. The strata are not usually much disturbed, and hence the dip is not great. At Thompson's Point it is only 8º, at Larabee's 12º, and. in few places is it more than 20°. The dip is usually towards the east, but in some place it is northeast or northwest. A few of the outcrops of the Chazy

GEOLOGICAL FORMATION OF THE COUNTY.

limestone are filled with fossils which are colored pink or red, and these, con- trasting with the gray of the main mass of the stone, are very conspicu- ous. In other beds the fossils are some of them red and some white, and some of these layers are almost entirely composed of fossils, either whole, or broken and comminuted. Many of the fossils are stems of crinoids, and these show as disks or rings in the stone. The marble which the Burlington Manufactur- ing Company sell under the name " Lepanto," is this highly fossiliferous rock sawn into slabs and polished. It is a very excellent marble, as it is handsome, strong, not easily stained, and most admirably adapted for mantels, furniture, or interior decorations, for which purposes it is very extensively used. There is a very good colored plate of this marble in Vol. X of the last Census Re- port, Plate 32. The entire mass is made up of comminuted fossils, and min- gled with the paste thus formed are numerous larger fragments, many of which are red, of different shades, others are white, and others are black. The gen- eral color of the marble is light gray in some slabs, and darker in others, and the effect of the fossils, all of which are small and of the colors just mentioned, upon this ground color is very fine, and the various slabs differ considerably in appearance. Not only in the beds used for marble, but in all the strata of the Chazy, the fossils are very small. There are a few exceptions. The maclurea and one or two orthocerata and corals are found of large size, but very few are more than a fraction of an inch in diameter. No strata of any age could con- tain more fossils than do some of those of this formation. Crinoids especially appear to have been very abundant, and as these animals are only found in clear, deep water now, we may believe that in ancient times they required the same conditions, and that the limestones of the Chazy were formed in such water, and other indications add probability to this view. Not always, however, or at least not in every locality, for, according to the Vermont Report, some of the strata on Isle La Motte have on their surfaces ripple-marks, mud-cracks, etc., which could only have been formed in shallow water ; but this is probably ex- ceptional. According to the same Report there is at Ferrisburgh and Panton a layer of Chazy limestone which is in part " a conglomerate formed from the ruins of Calciferous sandrock." Were there no other proof, this would be suf- ficient to show that the sand and mud of Calciferous time had, by this time, hardened into stone and fragments been torn away and mingled with the newly formed deposits of the Chazy. The subsidence which began with the Cam- brian period, and perhaps before, continued, probably with little or no inter- ruption, on through the whole of the Silurian, and it appears to have increased toward the latter part of the age, and, as epoch after epoch passed by, the seas deepened and the water grew clear, and with this change of condition a change took place in the rocks, sandstones and gritty limestones ; shallow water formations gave place to the deep water formations, shales and lime- stones, and in the Chazy and the following epoch, the Trenton, these rocks.

HISTORY OF CHITTENDEN COUNTY.

form the chief part of the rock mass. Over the United States the Trenton is more widely developed and a more important formation that the Chazy, but in the Champlain valley the reverse is the case ; yet in many places here this period is well displayed. The Trenton period is subdivided into three epochs, the Trenton, the Utica, and the Cincinnati, or, as it used to be called, and is still by some writers, the Hudson River. These three epochs are probably all of them represented in Chittenden county ; I say probably, because there may be some doubt about the last, though very little I think. The Trenton epoch is still further subdivided into the Black River and Trenton. The Black River formation is a dark limestone, and is found in this county only at McNeil's Point, I think, although narrow bands of it stretch southward as for as Lara- bee's, and on Isle La Motte there is an outcrop. This stone is often so dark that when polished it makes a jet black marble, and is used for that purpose. The fossils of the Black River are so similar to those of the Trenton that it will not be worth while to consider them separately. This Trenton formation is found outcropping in many localities all over the State from West Haven to Highgate. Some of the strata dip very little, while some dip very greatly, and some are almost vertical. Plicated and folded strata occur, especially in the northern beds. The most characteristic rock is a dark gray or black limestone, but a variety of other rocks is found in the formation, as the following list, taken from the Vermont Report, shows : -

" I. Black, shaly limestone. 2. Black limestone, compact and schistose. 3. Slaty layers, sometimes argillaceous. 4. Light blue, compact, schistose limestone. 5. Grey, thick bedded strata. 6. Ordinary limestone metamor- phosed into white, grayish white and dirty looking ferruginous strata, frequently with a net-work of calcite or quartz. 7. Bituminous and fetid layers. 8. Sandy limestones."

In this county the Trenton shows itself at Charlotte, at McNeil's Point. Here the strata have not been very much disturbed, and the dip is only from 9º to 15°. The Trenton runs along just east of the Calciferous from south of Shoreham to Charlotte where it comes to the lake ; from this point it extends un- der the lake and reappears on the New York side in large masses and at many points. It also appears on Grand Isle, and forms a considerable part of the north- ern end of Isle La Motte. So far as the rocks show, there was no great disturb- ance between the Chazy and the Trenton, and yet there must have been some change, for the life of the Chazy became extinct, and though in so many re- spects similar, the Trenton opens with a new array of animals. The continent was still small and no evidence has been discovered that there was any terres- trial life. Sea-weeds are the only plants, and even they are rare, and all the animals are marine. Many species have been discovered representing almost all of the lower orders. Corals, some of them of large size, are found. Mol- lusk abound so that some of the layers of rock are made up of shells cemented

GEOLOGICAL FORMATION OF THE COUNTY.

together, as if the ancient sea bottom was completely covered with them and then hardened to stone. Trilobites lived in great numbers in some parts of the seas, and huge orthocerata swam about, the largest and strongest of all, like huge shelled cuttle-fish, devouring all about them. Perhaps as common and characteristic a fossil as any found in the Trenton is a hemispherical coral two or three inches in diameter, looking somewhat like a puff-ball cut across. This is common at McNeil's. Another coral looks like a petrified honeycomb. The Vermont Report gives fairly good figures of some of the more common species of our Trenton fossils. The orthocerata attract much attention when seen, from their form and appearance. Some of them have been taken for petrified snakes, because of the long, tapering, cylindrical form, banded by the walls of the many chambers, in the outermost of which the animal lived, the rest of the shell forming a sort of float. Some of the trilobites of the Trenton are quite handsome, at least they are so to the eye of a collector. They are somewhat like gigantic pill-bugs, divided into three longitudinal portions and ' transversely ridged and ribbed. Some were ornamented with bosses and tubercles innumerable, others were decorated, if not armed, with spines. Some of them were very large ; the asaphusgigas, which is found in several of our Vermont localities, being sometimes eight or ten inches long and four or five inches wide. Most of these creatures, however, were only three or four inches long, and some were only a fraction of an inch. They probably resembled our modern crabs in their habits, as they did in structure. Sometimes they are found rolled up head and tail together. Entire specimens are not common, but portions, especially the hinder part, are quite abundant in some layers. In very few respects does the life of this period resemble that of the present. A few of the fossil shells remind one of those of mollusks now living; but most of the forms were long since destroyed, and their like has never been seen since.

The Utica is a much less extensive formation everywhere, and in this county it is exposed in not very large masses. It is especially a formation in which shale was formed. It is found as a black, slaty rock, readily splitting into thin layers, for the most part rather soft and brittle, and in some places, besides the change due to the lamination of the rock, there is a jointed struct- ure-due to lateral pressure, in all probability-a mass of strata when soft and yielding being squeezed by pressure from each side or end; and thus fine cracks are formed, and the strata themselves more or less folded. The regu- larity of some of these joints is very remarkable. The strata break crosswise into squares, triangles, and other shapes as evenly and regularly as if cut with a sharp knife when soft. At Ladd's, on Grand Isle, this structure is most admirably shown. Masses of iron pyrites are common in some of the layers of the Utica shale, sometimes deluding the unwary, by their golden color and metallic luster, with the idea that there is a deposit of the precious metal at 3

HISTORY OF CHITTENDEN COUNTY.

hand. Calcite is found in veins running through the shale, and some of these calcite veins are of considerable extent, and are very noticeable, since the lime carbonate is usually pure white ; and of course this shows distinctly on the black surface of the shale. Of these the Vermont Report remarks : "The veins of calcite form a marked feature of this rock. There are three varieties of them-the large veins or dikes, the smaller ones, that twist and branch in every direction, frequently like the branches of a tree; and thirdly, those small veins that occupy the cleavage seams, and are parallel to one another over large areas." The Utica shale is found in this county in Shelburne, Charlotte, Bur- lington, and Colchester. Juniper Island is chiefly of rock of this formation, and so is Rock Dunder ; and there is no doubt that other now isolated masses of this and other formations were once parts of a wide sheet, which has been all eroded except the small masses now found widely separated. Elsewhere in the State the Utica slate, or shale, is fairly well developed as far south as West Haven, and north to Isle La Motte and Alburgh. The rock is slaty in some places, shaly in others, and more rarely there is a little limestone; and it is chiefly in this latter that the pyrite mentioned above is found. It does not appear to be conformable to the Trenton-at least not always-and is usually more disturbed, the strata having a greater dip. In Charlotte this is 58º, and at Shelburne Point 41º 45', on Appletree Point 85º, and, as we go north from here, it is less until in some places the strata are nearly horizontal; on North Hero they are but 5º. Rock Dunder seems to be an upheaved mass ; at least there has been some upheaval, very likely, however, from lateral pressure ; for the rock composing it is folded, and therefore dips both east and west. The size of this mass of rocks of course varies with the state of the water. The Vermont Report gives the height, taken in July, at thirty-six feet, and the cir- cumference of the base three hundred and ten feet. At very low water these figures would need increasing, and at high water they would be too large. The life of the Utica is not extensive, though there are several very character- istic fossils. At the close of the Utica the shore of this county extended some- what farther west than now, the shore line reaching from Shelburne Point through Rock Dunder, Juniper Island, Appletree and Colchester Points, to South Hero and North Hero, swelling out to include Isle La Motte, and going on to Alburgh. All these islands and points were then joined to the mainland. The shore may have been still farther west, for we cannot know how far the rocks extend beneath the lake. The formation extends on from Alburgh to Montreal, and, following the north shore of the St. Lawrence, to the ocean. Not only this formation made a different shore line for this county, but time and again, as age after age passed, its contour and extent changed, now reced- ing from the lake, now extending farther into it; and thus although, as has been indicated, the deposits of the Cambrian largely determined what the county was to be, the present outline is by no means what it was during the past ages.

GEOLOGICAL FORMATION OF THE COUNTY.

The next and last epoch of the Trenton period is known as the Cincinnati, or Hudson River. This formation is probably an extensive one in the State and includes many kinds of rocks, some of them changed wholly, both in char- acter and appearance, by the metamorphic influences to which they have been exposed. A clay slate is perhaps the characteristic rock of the period, but limestone, sandstone, and various sorts of slate are all found, besides the meta- morphic rocks which occur in the Green Mountains. The various beds vary in color from light drab to black. Zadock Thompson thus describes its appear- ance in this county : "The black slate is generally contorted and crushed and abounds in seams of white calcite, varying from a line to a foot in thickness ; still there are places where the lamination has never been disturbed; but all this slate doubtless contains too much lime and is too brittle to be used for any better purpose than making roads. This slate in many places, particularly where it is fragmentary, has its surface covered with a black glazing, giving it very much the appearance of anthracite." The veins of calcite spoken of by Mr. Thompson are very familiar to any who have visited the shore of the lake at Appletree and Shelburne Points, or many other places where the beach is completely covered with pebbles of this rock; and they are also much used for covering walks. Any one who has chanced upon such a mass of these peb- bles or, better, seen a ledge of the rock from which the pebbles came, must have been amazed at the great variety and delicacy of this veining. Mr. Thompson puts the smaller veins at a line in width, but it is not at all difficult to find pebbles with much finer lines of the white than this; some can hardly be seen, they are so very slender. In this county the Cincinnati group is found at Charlotte, Shelburne-especially on the point-Rock Point, near Mal- let's Head in Colchester, at Stave Point north of Mallet's Bay, where it is a limestone and has been used for the manufacture of lime ; from here it goes on to Milton, Georgia, St. Albans, and Highgate, into Canada. Many of the smaller islands in the lake are of this formation, and probably more or less of what is now covered by the waters of Lake Champlain was at the close of this epoch dry land, for a time at least. It extends south of this county to the southern border of the State. In this county it usually, if not always, imme- diately overlies the red sandrock, showing that after the sandrock had been formed it remained above the sea where elevation of the sea bottom had placed it. During all the intermediate periods until before the Cincinnati, either dur- ing or at the end of the Utica, it again sank, in part, and upon it was deposited the material which made the later rocks. It should perhaps be noticed here that some of the beds which are included in the Cincinnati, or, as it is there called, the Hudson River, in the Vermont Report, do not belong to this forma- tion, as indeed the geologists writing the report appear to have suspected. The strata, like those of all the other formations in this county, dip in the main to the east. The amount of dip is very variable. In Milton it is 10°, in Shel-

HISTORY OF CHITTENDEN COUNTY.

burne 150-200, in Colchester, 700. The strike is chiefly northeast. Of the metamorphic rocks belonging to this group more will be said when we con- sider the formation of the Green Mountains. It is enough for the present to quote the following paragraphs from Professor Dana (Manual of Geology, 2d edition, page 195): "In the Green Mountains there are strata of mica, schist, gneiss, and quartzite, overlying the great Stockbridge limestone; and since they are quite certainly Lower Silurian, and at the same time newer than this limestone, they probably belong to the Cincinnati epoch." As we shall see later, Professor Dana has confirmed this opinion by further investigations, so that we may regard it as settled in his own mind.

The Cincinnati period shows us a great variety of living forms-corals, cri- noids, star-fish, mollusks, trilobites. With the close of this epoch we reach the close of the great Lower Silurian age. Although this is by no means a mod- ern time, yet all the solid rocks of this county and most of those of the State and of New England were formed before this period closed. Slowly, age by age, the rock masses that we now find in our ledges were laid down. The Silurian was a very long period, occupying millions of years; and during the slow passage of these ages the land was outlined, rose above and fell beneath the sea; group after group of strange animals appeared, lived out their cycle of existence, and gave place to new; change, progress, development-exceed- ingly gradual, perhaps, but none the less sure-were the ruling conditions. During all this time there is no evidence of the growth of any land plants or that any animals roamed over the bleak continent. All life was marine. Nor were there any animals of a higher grade than trilobites and orthoceratites. But this is not all ; vaster changes took place at the close of the Lower Silurian, which culminated in the Green Mountain range. The history of the Champlain valley and of that portion of it which makes up this county is like the history of the globe, one of commotion and change, of rock masses raised perhaps hundreds of feet, or sunk as many; of masses of rock of almost continental extent crushed, folded, and even overturned, so that the lower strata became the upper, sedimentary rocks, as limestones and sandstones are crystallized and changed beyond recognition, becoming schists, gneiss, marble, etc. In this county less violent upheavals and distortions of the strata have taken place than are found in many regions, and yet gigantic operations have been carried on here. During the ages of the Silurian and also of the Cambrian everything seems to have gone on quietly. The different groups of strata are not in all cases quite parallel, or, in geological phrase, conformable, showing, as in the case of the Utica and Trenton, that there was some upheaval after the deposi- tion of the lower and before that of the upper group; but in all cases, I believe, such phenomena are limited in extent and are not very pronounced-that is, the difference in the dip and strike of the strata of the two epochs is not great. And yet, although during the Lower Silurian no great display of the dynamic

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History of Chittenden County, Vermont, with illustrations and biographical sketches of some of its prominent men and pioneers, Part 3

Author: Rann, W. S. (William S.) Publication date: 1886 Publisher: Syracuse, N.Y. : D. Mason & Co. Number of Pages: 1054

Author: Rann, W. S. (William S.)
Publication date: 1886
Publisher: Syracuse, N.Y. : D. Mason & Co.
Number of Pages: 1054