History of Chittenden County, Vermont, with illustrations and biographical sketches of some of its prominent men and pioneers, Part 2

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 2

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GEOLOGICAL FORMATION OF THE COUNTY.

lect in these and leave the rest dry land, and thus the first oceans and conti- nents came into existence. At first there could have been only water and solid rock on the earth, but as soon as the water began to move in waves against the rocky shores, sand was formed; for sand is merely ground-up rock, and thus we have the beginning of dry land. Thus in its briefest outlines was the earth formed, or rather developed, during its earliest stages. Of all this there is no record, but there are many facts which give great probability to such a hypothesis.

The subdivisions of geological time spoken of above begin at the end of this first period, taking into account only those ages which are represented by rocks. Nowhere on the face of the globe are there exposed masses of rocks which are parts of the original crust of the earth, that which came from the cooling of the molten mass; for the oldest known contain fragments of yet older rocks and other proofs that before they were formed rock masses existed.

The following are the larger subdivisions used by most American geolo- gists: 1, Archan. 2, Paleozoic. 3, Mesozoic. 4, Cenozoic.

These are again divided each into several periods. Of these only two are represented in this county, the Paleozoic and the Cenozoic. The Archæan is finely exhibited in plain sight of many of the inhabitants of the county, for the Adirondacks are composed wholly of Archaan rock, and according to some geologists there are patches of the same age in this county on the flanks of the Green Mountains; but it seems most probable that these are of a later age. It is indeed possible that the Archaan rocks may extend under the lake and underlie some or all of our later formations; but it seems most likely that if this were so there would somewhere be at least one, if no more, tell-tale outcrop. The second grand division of geological time, the Paleozoic, is di- vided first into three ages, viz., the Silurian, Devonian and Carboniferous. The Silurian is divided into Lower and Upper. The Lower Silurian, which alone is found in this county, is divided into periods. These are: I, Primordial, or Cambrian .- A. Acadian. B. Potsdam. 2, Canadian .- A. Calciferous. B. Quebec. C. Chazy. 3, Trenton .- A. Trenton. B. Utica. C. Cincinnati.

It may be noticed at this point that Chittenden county has, so far at least as has been discovered, no wealth in mines or ores. Galenite, several vari- eties of iron ore, manganese, and some other metals are found, but in very small quantities, not at all in such masses that mining for them could be made to pay. So far as the county is rich in its rocks it is because of their value as building materials, not for any metal they contain.

We now come to the study of the development of this region from the time when its first beds of sedimentary rock were laid down, until the present. This is not by any means a simple task. Probably there is no region of equal size which has been more thoroughly discussed and concerning which so few defi- nite conclusions have been reached as Western Vermont. And although, as

HISTORY OF CHITTENDEN COUNTY.

seems, order is being brought out of this disorder, yet wide disagreement as to facts and the meaning of facts exists among American geologists. Almost ever since there was any American geology, for more than forty years at any rate, the age of the Green Mountains and of some of the terraces lying be- tween them and the lake, has been debated, and I do not suppose that all geol- ogists would admit that it is yet settled. Indeed no one can assert that the whole range can be shown to be of one age or another, whatever he may think as to the probability that it is this or that. Until within a few years our knowledge of the age of many of our Vermont rocks was exceedingly uncer- tain, but, through the labors of Professor C. H. Hitchock, and much more those of Professor Dana and Rev. A. Wing, very much information has been obtained and many important facts discovered, so that by the aid of these we may be- lieve that the age of most of our rocks has been satisfactorily determined. It is rather remarkable that after many trained geologists had gone over the ground and given few facts to help us solve the difficult problems which the rocks presented, a quiet, unknown minister and teacher should have taken up the work, and, persistently keeping at it season after season, should have made discoveries of the highest value and importance. Of this Professor Dana says: "Mr. Wing, by the use of his spare time amid the duties of teaching, accom- plished vastly more for the elucidation of the age of Vermont rocks than had been done by the Vermont Geological Survey. The Vermont Report presents diverse opinions about the Eolian limestone and the formations adjoining, but settles nothing ; while Mr. Wing's discoveries shed light not on these rocks alone, but also on the general geology of New England and eastern North America."1 The Vermont Report alluded to above was published in 1861 in two quarto volumes, and is quite as good as the State deserved, considering the amount of money appropriated to carry on the survey, but it is nowise worthy of the State and not at all trustworthy in regard to the age of many of the rocks of which it speaks; and scarcely a single one of the many problems which the study of Vermont rocks calls up is solved, or even helped towards solution by the explorations of those in charge of the survey. The Report does, how- ever, give many valuable details as to the distribution of rocks. In the second volume of Miss Hemenway's Gazeteer there is quite an extended paper by Rev. J. B. Perry, on "The Geology of Northwestern Vermont." In this an attempt is made to solve some of these problems; but the author seems to have been captured by his theories, which are many and peculiar, and the result is that the geology of the article is very visionary and unsatisfactory, and such as no geologist, I think, would for a moment accept. It may seem quite ungra- cious and possibly in bad taste for the writer of this article to find such fault with his predecessors, and he would gladly speak in a less unpleasant way if it were possible ; but I think that most geologists would justify the above state-

1 For a full account of Mr. Wing's discoveries, by Professor Dana, see American Journal of Science and Arts, Vol. xiii, pp. 332, 405.

GEOLOGICAL FORMATION OF THE COUNTY.

ments. And they are made not for the sake of criticism, but simply to pre- vent any one who may seek information on the works named from being greatly misled, as he certainly would be if he put his trust in either. About all that has been published concerning the geology of Western Vermont that is of much value, so far as the age and relative position of the strata go, is to be found in various articles published by Professor J. D. Dana in the volumes of the The American Journal of Science and Arts, published during the years 1872-1880. After what has been said above, it is scarcely necessary to add that the views of Professor Dana and Mr. Wing will be followed in general through- out this chapter ; for it is believed by the writer that they are the only ones which rest upon a substantial basis and which will stand the test of future in- vestigations.

The geological history of this county and of nearly the whole State begins with the beds of Cambrian rock. In Southern Vermont there are limited areas of rocks probably older than these, but I think there are none older in the northern part of the State. At this time most, perhaps all, of not only this region but New England, was covered by the well-nigh universal ocean. The continent of North America was very small, and chiefly north of the present United States in Canada, with a long, narrow southern prolongation along the Adirondack region, and isolated islands here and there over the present terri- tory. Probably the Champlain valley was not marked out, except on its west- ern border, and Lake Champlain did not exist until long after this. Possibly beneath the schists, slates and gneiss of the Green Mountains there is an axis of Archæan rock; but it is not shown by any evidence now obtainable. If there were such an axis it would have been a low reef at the time of which we are speaking, dimly marking out the eastern border of the valley which was to exist later. The waves of the great Archaan ocean dashing against the Ad- irondacks, and whatever other rocky shores there were, ground them to sand, and this sand scattered over the bottom of what was probably a shallow sea, gradually became sandrock, in which some bits of sea-weeds, a few shell-fish, and now and then a trilobite were imbedded; but for the most part no living beings were added to the forming beds of rock. This rock is now found at Keeseville and the Ausable Chasm, as well as in many other localities on the western side of the lake; and on this side it is our red sandrock, so largely ex- posed in this county, such as is seen at Willard's Ledge, Red Rocks, etc. The red sandrock of Western Vermont-for it extends from Shoreham north- ward through the State to Canada-belongs to the Cambrian period. It is usually a hard, silicious stone of a dark red color, but this is very inconstant ; for although great masses may be found which are throughout of this dark red, there are also frequent outcrops of all shades from dark red to the most delicately tinted flesh color. Other layers are buff or even gray. Nor is the rock always a sandstone, as the following section will show. Although this

HISTORY OF CHITTENDEN COUNTY.

section is taken north of the county near Swanton, yet I give it, since it shows the whole structure of the formation better than any section that could be ob- tained here. This section was taken by Sir William Logan, geologist-in-chief of the Canada survey.

Feet.

I. White and red dolomites (Winooski marble) with sandy layers ; some of the strata are mottled, rose red and white, and a few are brick red or Indian red. Some of the red beds contain Conocephalites adamsi and C. vulcanus.

370

2. Gray argillaceous limestone, partly magnesiau, holding a great abundance of Palæophycus incipiens ITO

3. Buff sandy dolomite.

4. Dark gray and bluish-black slate, partially magnesian, with thin bands of sandy dolomite. The slate contains fossils, as Obollela cingulata, Orthisina festinata, Camerella antiquata, Conocephalites teucer, Paradoxides thompsoni, P. vermontana.

130

5. Bands of bluish mottled dolomite, mixed with patches of pure gray limestone and gray dol- omite and bands of gray micaceons flagstone with fucoids.

60.

A mile or so north of the above section other strata occur, as follows :

6. Light gray more less dolomitic sandstones and " some of which are fine grained, others are fine conglomerate." These are interstratified with bands of white sandstone ..

7. Bluish thin bedded argillaceons flagstones and slates, containing Conocephalites arenosus and fucoids 60

8. Bluish and yellowish mottled dolomite.

120

: 9. Yellowish and yellowish-gray sandy dolomite 600

Still further north, on the Canada line, there are additional strata, though not well exposed; but in general Sir William gives them as follows :

630

IO. Buff and whitish sandy dolomite, holding a great amount of black and gray chert in irreg- ular fragments of various sizes up to a foot in length and six inches wide. There are also masses of white quartz. Thickness (conjectured). 790

In some ledges near Burlington the sandrock becomes an impure, dark brown limestone, or if not replaced by it, it is interstratified with it. North of Burlington, at Mallet's Bay, it becomes calcareous and brecciated and is the Wi- nooski marble. In Milton it is a calcareous sandrock, while in Hinesburg it is- a clearly defined limestone, so much so that it serves a good purpose for the manufacture of lime. As in many of the ledges stone can be readily obtained which splits and breaks into fairly regular rectangular masses, the red sand- rock is a very valuable building stone. It is also very durable and handsome, though its color is not always unchanged after exposure to the weather. The entire formation is about two thousand feet thick, but in no one locality does it show any such thickness. The strata of red sandrock dip easterly at varying angles in different localities. At Red Rocks the dip is 90°; but usually the dip is much less, as in New Haven it is but 5°; in Monkton different strata dip 15º 20°, 50°; in Charlotte the dip varies from 15° to 80º. In Monkton the layers are found upheaved so that they slope each way from a central ridge. These anticlinals all have north and south ridges, the strata of course dipping east and west. It may be well to explain that in geology by the term "dip " is meant the inclination of the strata to the horizon. It is sometimes of value to know the strike, and this is the general direction of the outcrop or mass and is

GEOLOGICAL FORMATION OF THE COUNTY.

always at right angles with the dip. Stratified rocks are believed to always re- sult from the deposit of sediment in water, and hence the strata must have been originally horizontal or nearly so; therefore the amount of dip and strike indi- cate somewhat the extent of upheaval, displacement, etc., which has taken place since the strata were deposited. As a whole the red sandrock formation seems to be more silicious in its southern portion and more calcareous in its northern. The individual strata vary greatly in thickness, some of them being but an inch or so, while the thickest are several feet. The color is due largely to iron ox- ide, and the rock also contains magnesia, lime, potassa, soda and alumina. The composition, however, is far from uniform in different layers. As a building stone the red sandrock will probably always have its chief value; but the char- acter of some of the beds is such that more than a passing mention is deserved. I refer to the layers known as the Winooski, or Wakefield, marble. These beds begin between Burlington and Mallet's Bay, and extend beyond St. Albans, where, between that place and Swanton, the Messrs. Barney have quarried it for many years. The " marble " layers differ from the sandrock, into which, how- ever, they pass by imperceptible gradations, in that they contain much more lime and less silica. An average specimen contains ten per cent. of silica, forty per cent. of lime carbonate, thirty per cent. of magnesia carbonate, with a smaller percentage of iron and alumina. Several times during the last thirty years at- tempts have been made to quarry, saw and polish the stone from Mallet's Bay. So far as the beauty of the slabs is concerned these attempts have been most completely successful ; but the cost of working so hard a material has in all cases proved an insuperable obstacle to carrying on the work extensively. And this very difficulty has its offsets, for, being hard, the stone takes a brilliant polish and it is not so easily scratched or otherwise marred as is a softer marble. Probably there is nowhere a finer deposit of ornamental marble than this, nor one which affords so great a variety in shade and pattern. It has been used in some of the largest and finest public buildings, as the capitol at Albany, Astor Library, and others, for inside decoration. It is not to be recommended for outside work, since its brilliant colors fade when exposed to all weathers. The marble crops out on the shores of Mallet's Bay as bold headlands from one hundred to two hundred or more feet above the bay, and also forms islands in the bay, and hills back from it. So near the water are some of these cliffs of marble that boats could be loaded by the same derrick that swung the blocks from the quarry. Some of the masses are regularly stratified, and thus easily separable into blocks, while others are not so ; but blocks from which large slabs, sound throughout, may be sawn, are abundant. No one can form an adequate idea of the unend- ing variety which is found in this marble, unless he has visited the locality and seen it with his own eyes. The range of color is not very great, but of shades and combinations there is no end. Red in all possible shades and tints is per- haps the predominant color; while common, though less abundant, are various

HISTORY OF CHITTENDEN COUNTY.

olive tints, drab, yellow and brown, all of them more or less mingled with pure white. There are in the Report of the Tenth Census, Vol. X, four colored plates which give a very excellent idea of this marble, though of course showing only four of the many varieties. The slabs may be very different, as they are sawn transversely or perpendicularly to the plane of bedding, and any change of direc- tion given to the saws as they go through a block changes, sometimes very re- markably, the appearance of the marble, and not infrequently opposite surfaces of the same slab may differ not a little. This is possible partly because many of the layers are brecciated, white or light fragments of older rock being im- bedded in a red sandy mud, and the whole hardened to stone. As these in- cluded fragments are of all shapes and sizes and very irregular, it is obvious that no two slabs can be precisely alike. Not all the stone shows this feature. In some the colors are more or less shaded or clouded, showing that the various components of the stone were thoroughly pulverized before consolidation. In some cases it is evident that a large included mass was broken after it was im- bedded, but before the paste became hard ; for the several fragments may be seen near each other, though not quite in contact.

It is very difficult to describe such a stone as this in such a vivid manner as shall bring it clearly before the reader ; but as most of my readers will be resi- dents of Chittenden county and presumably more or less familiar with the stone, I may hope to at least call attention to the more prominent varieties. In the first place we may arrange our specimens in several series, though without en- tire accuracy, for that is impossible in so variable a material. In one series we may include such varieties as present the red shades clearly and decidedly. In this group there are many varieties, from those in which the red is like jasper or Indian red, to those in which it is a delicate rose, or pink, like the lining of a shell. In a second group we may place numerous specimens in which the red is always of a brownish or chocolate hue, sometimes very dark, and from this graded through lighter shades until it becomes almost white. In a third series we may place such specimens as exhibit the red shades to a much less degree and have mingled with them other shades, as olives, greenish-drab and lavender. It is easy to understand how the great variety already mentioned is produced by these shades in constantly varying combinations and proportions, mingled with white in the blotched, shaded or brecciated masses. We find light colors mingled with a greater amount of dark or the reverse, large blotches or small, etc., etc.

Nearest Burlington-that is, nearest the layers of the typical red sandrock- the layers of marble are nearly all red with a few clear white veins of lime car- bonate, and sometimes sprinkled with little bits of translucent quartz. This variety is harder than any other and has been very little used. A softer though similar variety is not veined, but clouded and blotched with the lime carbonate. Another mixture of red and white is one of the richest and handsomest of all

GEOLOGICAL FORMATION OF THE COUNTY.

the varieties. In this the well-defined red shades are in many bands, dark and light, and these bands are intermingled in very complex patterns, and across them are numerous fine lines of clear white lime carbonate. I have seen slabs of this eight feet long and over five feet wide. Such a slab when brilliantly polished, as it may be, is unequaled in elegance by any marble that I have ever seen. Those specimens which would come under the second head are col- lectively called by the marble workers " chocolate." These lack the brightness of the other classes ; nevertheless some of them are very handsome. In delicacy of shading and exquisite combination of tints the lighter varieties excel. In some of these the darker shades are mostly lacking and the stone presents a surface blotched and mottled with small irregular patches of pink or flesh color, light tan, lavender and white. In some cases the effect is heightened by irreg- ular lines of dark green or olive, sometimes so dark as to be almost black. In some the dark shades of red appear, but only as lines or small spots ; and with these pink, salmon, rose and white are delightfully blended. One of the most charming slabs I have seen was daintily mottled and blotched with lavender and " ashes of roses " so abundantly that these tints gave tone to the whole surface, while mingled with them were bits of salmon and rose-flecked white.

Another peculiarly beautiful variety shows the red largely replaced by drab tints and white. But one familiar with this marble might go on until he had wearied his readers beyond endurance, and yet not exhaust his material, al- though very likely his stock of adjectives would soon grow small. All of these varieties that I have mentioned are found at Mallet's Bay. Other parts of the same formation are somewhat different. Some of the pieces remind one of ag- ates and jasper, which stones they quite closely resemble both in color and brilliancy of polish. At present no large quantities of this marble are used for, owing to its silicious character, the marble workers do not like to saw it; but it seems wholly improbable that so wonderfully varied and so beautiful a marble, and withal so durable, shall be left unused for a great length of time. We may hope that the time will come when one of the important industries of this county will be quarrying and working the Winooski marble.

The red sandrock as a formation has not yielded many fossils and those that have been found have been obtained in a few localities. By far the greater part of the formation appears to be destitute of fossils. I am inclined to think that this absence of fossils is apparent rather than real. The fossils that are found at Highgate and elsewhere are casts and only seen when the rock has been weathered for a long time. Hence there may be layers full of fossils which we do not see, because the fossil is so exactly the color of the rock, but which might be made evident by years of weathering. At Willard's Ledge the surface of the layers is glossy and undulating as if the rock were hardened mud, as it is, and this appearance, together with various seams which show where cracks made by drying in the sun have been filled, show us that the formation origi-

HISTORY OF CHITTENDEN COUNTY.

nated in shallow water. At Willard's Ledge and elsewhere sea-weeds are not uncommon. The most prolific locality is at Highgate, near the springs, where trilobites and mollusca of the genera conocephalites, camerella, orthisina, orbol- Lela, etc., are found, and in a ledge of brown shale at Georgia great trilo- bites, paradoxides, etc., are found. In the dolomitic limestone, which we have called Winooski marble, there was discovered a few years ago a little cyl- indrical fossil known as salterella pulchella. This occurs very rarely, but in those slabs in which it is found it is usually quite abundant. It is impossible to find it except as the slabs are sawn. In the Archaan rocks some evidences of life are found, but they are for the most part meager and uncertain. At the commencement of Lower Silurian times, however, there seems to have been a great variety of animal forms. If we let our imagination carry us back over millions of years, to the time when beneath the waters of the Silurian ocean the various beds of the Cambrian were being laid down, when Vermont was not yet above the water, we may see creeping over the Adirondack shore, or the shal- lows on this side, the trilobites, ancient representatives of crabs and lobsters, some of them six inches or more in length, sponges growing on the rocks, a few snail-like mollusks creeping hither and thither, and a few orthocerata -the high- est forms of life then existing - swimming through the waters. These ortho- cerata are conspicuous throughout the Silurian. They were animals much like the cuttle-fish, except that they had long, straight, chambered shells, in the last chamber of which they lived. Could we have looked over that landscape our eyes would have rested on no green thing ; for no land plants appeared till long after this. We should have seen only an almost limitless waste of waters, with here and there small masses of land rising above it. And yet a varied, and very probably abundant, life inhabited the desolate ocean. It is very remarkable that life should, to all appearance, have come upon the globe almost at a bound. Instead of a few of the lowest forms such as we should expect to find, after the meager beginnings in the Archæan rocks, we find, not the highest animals cer- tainly, but a great variety of forms, many of them by no means the lowest in the scale, and representing all the great groups of animals except the highest, the vertebrates. A mere list of all the Cambrian species would occupy much space. During this period the climate was probably mild and not given to change ; thick fogs and mists hung over the ocean, obscuring the sun, though that there was light seems to be shown by the trilobites, for they have well- formed eyes, compound and prominent ; and these organs could have been of no use had there been no light.

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History of Chittenden County, Vermont, with illustrations and biographical sketches of some of its prominent men and pioneers, Part 2

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