USA > New Hampshire > Cheshire County > Gazetteer of Cheshire County, N.H., 1736-1885 > Part 3
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CHESHIRE COUNTY.
The Ashuelot is one of the most important streams, of its size, in the state, in point of improved water-power. Its source is from ponds in Washington, Sullivan county, and flowing thence, in a southwesterly direction, through Marlow, Gilsum, Surry, Keene, Swanzey and Winchester, it empties into the Connecticut, in Hinsdale, near the Massachusetts line. Its principal branches are a stream coming from Stoddard, through the northwest corner of Nelson, southeast corner of Sullivan, and northwest corner of Roxbury, to Keene ; and one from Dublin, through Marlboro, to South Keene, where it joins the stream coming from Stoddard. Also a stream comes from Troy, through the southwest corner of Marlboro, and joins the Ashuelot in Swanzey. Nearly all of these sources are from ponds which have been dammed, thus producing large reservoirs and affording constant water-power to the manufactories on the stream below. The length of the river is about forty miles, and it drains a basin of 240,000 acres, or 375 square miles. From its source to the Con- necticut it has a fall of nearly 1,000 feet.
Cold river has its source in Unity, Acworth, and the southwest corner of Lempster, in Sullivan county, and thence passes through the southerly part of Langdon and the northwesterly part of Alstead, falling into the Con- necticut in the northerly part of Walpole. It drains a basin of nearly 60,000 acres, and affords some valuable mill privileges.
Several branches of the Contoocook water three or four towns in the east- ern part, affording some of the best water-powers in the county. There are numerous other streams, and many beautiful lakelets and ponds, which are described in the sketches of the several towns.
GEOLOGICAL.
A study of the science of Geology-"The footprints of the Creator"-is to most people ever an interesting one; and the charm experienced by a student of this subject as he wanders adown the musty eons, noting here and there the changes that the Deity's laws have wrought since He first said "let there be light," should be a stranger to none. In the following remarks on the sub- ject, as related to Cheshire county, our readers will doubtless derive a two- fold pleasure : first, the section under consideration is to them that small, yet large, part of the earth's crust called "home"; second, their journey will be conducted, in most part, by a no less able and worthy guide than Prof. Charles H. Hitchcock, of Dartmouth college. The first cannot fail to excite interest -the second cannot fail to be interesting. Before placing ourselves under our guide's care, however, a brief glance at the fundamental principles of the science may not be superfluous.
Among men of science it has become the common, if not the prevailing opinion, that in the beginning, all the elements with which we meet are in an etherial or gaseous state-that they slowly condensed, existing for ages as a heat- ed fluid, by degrees becoming more consistent-that thus the whole earth was
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CHESHIRE COUNTY.
once an immense ball of fiery matter-that, in the course of time, it was ren- dered very compact, and at last became crusted over, as the process of cool- ing gradually advanced, and that its interior is still in a molten condition .. Thus, if the view suggested be correct, the entire planet in its earlier phases, as well as the larger part now beneath and within its solid crust, was a mass of molten fire, and is known to geologists as the elementary or molten period. Following this came another age, in which the molten mass began to cool and a crust to form, called the igneous period. Contemporaneous with the begin- ning of the igneous period came another epoch. The crust thus formed would naturally become surrounded by an atmosphere heavily charged with minerals in a gaseous or vaporous cor.dition. As the cooling advanced, this- etherealized matter would condense and seek a lower level, thus coating the earth over with another rock. This is named the vaporous period. At last, however, another age was ushered in, one altogether different from those which had preceded it. The moist vapor which must of necessity have per- vaded the atmosphere, began to condense and settle, gathering into the hol- lows and crevices of the rocks, until nearly the whole surface of the earth was. covered with water. This was called the aqueous period. As these waters began to recede and the "firmament to appear," the long winter that inter- vened while the sun was obscured by the heavy clouds, would shackle the earth with mighty ice floes and glaciers, forming a drift or glacial period. A great difference also exists in the consolidation and structure of the deposits thus formed. The very newest consist of unconsolidated gravel, sand and clay, forming alluvium. A little further down we come to the tertiary strata, where are some hardened rocks, and others more or less soft. Next below the tertiary are found thick deposits, mostly consolidated, but showing a mechan- ical structure along with the crystalline arrangement of the ingredients. These are called secondary and transition. Lowest of all are found rocks having a decidedly crystalline structure, looking as if the different minerals of which they are composed crowded hard upon one another. These rocks are called metamorphic, hypozoic and azoic. We will now listen to Prof. Hitchcock.
BEGINNING OF DRY LAND.
In another place (Vol. I., Geology of New Hampshire) I have given a series of maps showing how the dry land of the State has been gradually reclaimed from the primitive ocean, beginning with the areas of porphyritic gneiss. I have latterly gone further and claimed that these same areas, with others like them, constituted the nucleus of the North American continent. It would seem as if these projections, or islands, were of eruptive origin, very much like submarine volcanoes, the first that appeared after a crust had formed around the earth. Later ejections increased their dimensions and sediment came down the slopes so as gradually to unite the cones. A continuation of the earth's contraction would tend to raise the earlier heaps of eruptive debris and thus to construct a continent. This view gives us the advantage of fix-
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CHESHIRE COUNTY.
ing upon the very beginning of terrestrial accumulation, instead of being forced to imagine a basin in which these earliest accumulations were de- posited as sediment. As this theory has been broached but recently, a few points may be cited in its favor, as follows :-
First :- Considering the igneous nature of the earth, volcanic energies would naturally continue their action as soon as there was a crust to be broken through, and immense molten floods would ooze through the fissures. We are now beginning to understand that the numerous granites, syenites and porphyries of our region were eruptive, and that the older the period, the more numerous the igneous rocks.
Second :- We have found ovoidal areas in Cheshire county of both the old- est and later gneisses, while they are very numerous in other parts of the State. A careful study of some of them reveals a concentric structure, just such as would arise from the accumulation of molten rock, rather than from sedimentary deposit. Doubtless this concentricity will be found in all these areas when minutely studied. A somewhat similar structure is apparent in large vol- canoes like Vesuvius. Should that volcano cease to be active, rains would obliterate the craters and reduce the lava to a rounded dome, which, when cut into, would show concentric layers of differently constituted aggregations.
Third :- The difficulty in deciding whether our oldest group is granite or gneiss from an inspection of its crystalline particles, is just what may be expected upon our theory of its origin. Furthermore, all the special mineral peculiarities of true eruptive granite are to be noticed in our rock. Hence we would say that gneiss is derived from granite by pressure, rather than that granite is gneiss melted down.
Fourth :- The analogy of the origin of oceanic islands at the present day, suggest the igneous derivation of the laurentian areas. Most of the high islands of the Pacific are composed of lava, built up from submarine volcanoes ; and the lower lands may have been the same originally, supple- mented by the labor of coral animals. The size of a cluster of Pacific islands is certainly not inferior to that required to equal our American granite areas. The Hawaiian islands have a base of 100,000 square miles, which exceeds the dimensions of New England.
THE AGE OF ICE.
Volumes would be required to present all the facts of interest respecting the cold period, known as the Age of Ice. Our country was overspread by this glacial sheet shortly before the introduction of man, and its relics are seen in the smoothing and striation of the rocks and the universal disper- sion of bowlders. When the cold attained its maximum the direction of the current seems to have been to the southeast, though later there were local deviations, and most especially one mass filled the Connecticut valley to the depth of 1,000 feet. A few facts seem to indicate that a tributary glacier to the Connecticut flowed down the Ashuelot valley. Few localities exhibit
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CHESHIRE COUNTY.
finer glacial markings than Mt. Monadnock, which is completely covered by them from top to bottom. Those upon the northern side point up the moun- tain in a southerly direction, while those upon the south slope, even to the summit, have been crowded around in a southeasterly direction. At a later period in the glacial era, the ice seems to have curved around to the east side, instead of sliding over the summit.
When the warmer climate returned, this immense sheet of ice melted and enormously increased the size of our rivers. The Connecticut was a roaring flood 245 feet higher than now at the mouth of Cold river, 150 feet at Brattle- boro, over 200 feet at the mouth of the Ashuelot, and about 150 feet as it passed into Massachusetts. The immediate result of this freshet was the filling of the bottom of the valley with a blanket of sand, gravel and clay. As the water diminished in volume, it cut through this flood-plain and carved out the terraces which now line the sides of the valley and furnish the beau- tiful sites of several of our villages.
NATURE OF THE ROCKS.
Leaving these formative periods, we will now turn directly to the rocks of the county. The whole of Cheshire's territory is underlaid by crystalline rocks. Forty years ago most geologists would dismiss the subject very sum- marily by saying that it is all primary or granitic, and then mention the localities of various interesting minerals. It has been our task, however, to search into the distribution of the various rock-masses, so as to discover how the county has been gradually built up. While most of the rock may be termed granite, there are perceptible differences in it. One part may be a fine- grained rock, suitable for the manufacture of monumental objects ; another may be chequered by thousands of angular crystalline blotches ; a third may have the mica changed into some mineral of different composition ; while a fourth may be described as a dark slaty mass composed of bands of varying hardness. Such variations of form and appearance may be readily distinguished, and, when discovered, we can learn which is the old- est and conjecture the methods of original formation and subsequent history. The use of technical terms, in some cases, will be necessary to define clearly what is meant.
Topography .-- The foundation for a correct knowledge of the relative position of the rock formations is to be seen in the arrangement of the mountains and valleys, or the topography. A high conical mountain is usually composed of a rock different from that which surrounds and underlies it. It is the fact of some element of durability present which has prevented the mountain from yielding to disintegration and crumbling down to a plain. Valleys may orig- inate either because erosive agencies have carved out the depression, or because the surface was naturally low. In Cheshire county there are two topographical features of structure of the highest importance, determined
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CHESHIRE COUNTY,
primarily by the nature of the underlying rocks. The first is the high ridge of land constituting the water shed between the drainage of the Con- necticut and Merrimac rivers, while the second is the Connecticut valley, whose eastern slope makes up the greater part of the area. A few of the elevations illustrating these structural lines may emphasize the statement, as follows, arranged in order from north to south :--
LOCALITY.
Town.
Feet above sea level.
Pitcher Mountain
Stoddard.
2,170
Postoffice
Stoddard.
1,450
Mt. Stoddard.
Stoddard.
1,700
Summit of proposed Forest Line of railway
Stoddard.
1,560
Osgood and Hurd hills
Nelson.
1, 800
Summit of railway
Harrisville.
1, 265
Mt. Monadnock.
Dublin.
3, 169
Summit of Monadnock railway
Rindge.
1,127
The height then passes into New Ipswich, whose apex is to be seen in Barrett mountain, 1,847 feet, and at the state line the altitude is 1,500 feet. The lowest points in this ridge have been utilized for the passage of the two railroads, while the third finds its summit just south of the state line, at Ash- burnham. The heights along the Connecticut are less variable, as follows: Head of Bellows Falls
283 ft.
Foot of Bellows Falls
234 ft.
Walpole 226 ft.
Westmoreland 213 ft.
Chesterfield (Brattleboro)
200 ft.
Hinsdale and Vernon
187 ft.
State line
180 ft.
The fall of the river is therefore but a trifle above one hundred feet, or ex- cluding Bellows Falls, an average slope of about one and a half feet to the mile.
The crowning ridge in the eastern part of the county is supposed to be underlaid by the oldest group of ledges known. It was the first dry land raised above the ocean, and constituted the nucleus of the terrestrial area through all geological time. This ridge may have been temporarily submerged at different periods, especially at the time when the sediments composing Mt. Monadnock were deposited. As this primeval ridge has always been elevated, so the Connecticut Valley has always been a depression. It carries the newest rocks of the county, and has always drained the highlands to the east, west, and north, when the country has not been submerged.
Classification .- The following terms may express the classification of the rocks of the county by age, the oldest groups being mentioned last :- "
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CHESHIRE COUNTY.
Paleozoic.
Coös group, quartzites and mica schists.
Kearsarge group and fibrolite mica schist. Huronian. Montalban, upper laurentian.
Eozoic.
Lake group,
Bethlehem group,
middle laurentian.
Azoic.
Porphyritic gneiss, lower laurentian.
The lowest group .- The oldest rock seen anywhere in the county or state is a very coarse gneiss or granite. The minerals being alike in both these crystalline aggregates, it is necessary to determine whether they are arranged in parallel lines or are promiscuously mixed together, if we would say gneiss or granite. Well defined ledges of this age are easily recognized because of the large quadrangular blotches of light-colored feldspar which thickly pepper the mass and render the surface as conspicuous as the figures of a patchwork bed-quilt. These crystals vary from half of one to three inches in length. Quartz and feldspar are the essential constituents of the rock, while the third is commonly white mica, and rarely hornblende or chlorite. Black mica is the most common. Examination with a compound microscope sometimes re- veals the presence of apatite in fine needles, and long slender hairs of rutile in the quartz. The crystals of feldspar are often twinned, that is, they have been bisected along their greater length and one of the halves has been turned half way around, so that they do not match, and consequently reflect light differently on each side of the dividing plane.
This rock is often said to be porphyritic, because of a general resemblance to porphyry. A true porphyry consists of crystals, however, usually feldspar, scattered through a fine grained matrix of the same composition ; but our gneiss possesses a matrix composed of crystalline particles. It would be nearer proper to speak of it as an imitation, false or pseudo-porphyry. A German name for a part of it is augen or eye gneiss, because a superadded grouping of mica scales causes the white crystals to appear like eyes staring at the observer. If we carefully explore a section of this fundamental rock, we shall be perplexed to separate the granite from the gneiss, the two seem- ing to be interlocked and commingled inextricably. Probably the granite was the earlier condition of the two, and the gneiss was developed by pressure. Fragments of a dark schist are sometimes intermingled.
The eastern part of the county, comprising parts of Jaffrey, Dublin, Harris- ville, Nelson, and Stoddard, rests upon the edge of the largest area of this rock yet mapped in New England. The area is sixty-one miles long and fifteen wide, reaching nearly to Baker's river in Groton. A smaller but very interesting area of it forms the elevated and rugged portions of the towns of Chesterfield, Swanzey, Winchester, and Hinsdale. At Ashuelot village, in
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CHESHIRE COUNTY.
Winchester, the river has cut deeply through it. Smaller patches occur in Fitzwilliam, Jaffrey, and Marlow.
A singular feature of this water-shed, or back-bone, of the state, is that a geological section through it may exhibit what is called the fan-shaped strati- fication. The strata on the flanks dip toward the centre line, as if the middle were the newest part of a basin, and consequently newer than the outer edges. A careful study of this and similar cases, especially in the Alps of Switzer- land, shows that the original mountain fold has mostly disappeared. It was a gigantic loop, bulging at the top, and compressed where the present surface intersected the curve. The upper swollen portion has been removed by de- nudation, leaving the outer strata dipping toward each other.
Gneiss and Protogene .- Two distinctions were made in our published map of an immense belt of gneiss, 18,000 feet thick, which overlies the porphyritic gneiss upon both sides, viz .: the Bethlehem and Lake Winnipiseogee groups. The first is characterized by its oval appearance in considerable areas along the Connecticut, while the second may be continuous for sixty, eighty or one hundred miles. The Bethlehem rock is a protogene gneiss, or granite, nearly as indefinite as the lower laurentian. In Cheshire county the larger area ex- tends from the state line to Surry, through Winchester, Richmond, Swanzey, and Keene. The rock differs from ordinary gneiss by having its accessory mica or hornblende altered to chlorite or talc. In the Mt. Franklin granite, of Swanzey, deep brown hornblende, epidote, garnet, and plagioclase feldspar also occur. In Surry and Keene the protogene is often of a deep red color. It is supposed that this protogene is the same as ordinary gneiss, having undergone a special change in its mica, by some cause acting over several square miles of surface ; hence,it is not easy to say that the Bethlehem group is really dif- ferent from the Lake group, which succeeds the protogene at Surry, and passes northerly through the northern part of Cheshire into Sullivan county. Beds of limestone, magnetic iron and graphite or plumbago are liable to occur in this group, and may be looked for in Cheshire, though not known to exist. A small protogene area in Hinsdale and in Vernon, Vt., throws light upon the relative age of these rocks. The protogene is the central mass, girt by horn- blende schist, and that by quartzite. So great pressure has been exerted upon this section that the western bands of hornblende and quartzite have been forced to dip beneath the protogene, as well as their own repetitions. Such an arrangement of strata we call an inverted fold.
Hornblende Schist .-- This same hornblende rock is found encircling the larger area of protogene from Surry to Spafford Lake on the northwest, and to Richmond on the northeast side. It is also found capping the ordinary gneiss on the west side of the Connecticut, as well as farther north. Because of the difficulty of separating it from the Huronian north of Bellows Falls, we have classed it with that system in the State report. It is often 1,500 feet thick.
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CHESHIRE COUNTY.
Montalban .- The schists next in order are called montalban, and they occu- py a greater surface area than any other rock in the county, being situated in one tract between Stoddard and the State line, in the towns of Rindge, Fitz- william, Richmond, Troy, Jaffrey, Marlboro, Roxbury, Sullivan, Nelson and Stoddard. These rocks are feldspathic and ordinary mica schist, with the mica in large spangles, either black or white. A variety in which the quartz predominates, is heavily charged with minute particles of iron pyrites. On exposure to the atmosphere the pyrites decomposes, the rock crumbles, and the soil is colored a reddish-yellow from the presence of the iron peroxide. Rindge is very largely underlaid by this ferruginous variety of the mica schist. The name Montalban means White Mountains, and this rock in Cheshire is believed to be of the same age with that which composes the presidential range of summits. It also closes the series of ancient gneiss. The Cheshire range seems to be a great blanket resting unconformably upon the two older series. Owing to the abundance of the ferruginous member, this is not an agreeable formation to study in the field.
Huronian .- Following these imperfect gneisses is an extensive series of green schist and quartzites interlaminated with igneous rocks, very common in New Hampshire and Vermont, which we have referred to as Huronian. A belt of it commences in the northeast corner of Westminster, Vt., less than half a mile from this county, which follows the Connecticut to its source, and further, even to the Gulf of St. Lawrence. It was made prominent by the volcanic period in the geological history of New England. Closely related to the Huronian are two belts of rock in Cheshire county, peculiar as to their constituent minerals, but developed in the same period, apparently. The first is a micaceous quartzite full of the mineral fibrolite, about two miles wide, and crossing through Marlow, Alstead, Gilsum and Surry. This band frequently carries gigantic veins of granite in which the mica plates are large and sound enough to furnish "glass" to the hardware dealers, and has been mined for this purpose in Alstead. The other band has been called the Kearsarge group, and is developed upon Mt. Monad- nock. The rock is rather more sandy than the first named belt, and at many localities the fibrolite is replaced by pencils of andalusite, a mineral of essentially the same composition but different crystalline form. Monadnock is entirely composed of it, and the mass has a monoclinal structure with a moderate dip to the north and northwest. The cone of 2,000 feet altitude rests upon a montalban plateau 1,000 feet above the sea. The elevation is drawn out to the southwest in Gap mountain, making the extension of this andalusite rock about twelve miles. Monadnock is the most conspicuous elevation of the great primary water-shed, and its unusual altitude is due to the piling up of these schists upon the fundamental plain. Mt. Kearsarge, in Warner, Merrimac county, 30 miles away, is composed of he same material and is similarly isolated, though occupying a broader area. It is very likely that these two mountains were once united, and that the
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CHESHIRE COUNTY.
intervening rock has been swept away by powerful denudation. It is unusual to find proof of such an enormous erosion of material as this.
Coös Group .- The latest group of rocks known to exist in Cheshire has received from us the name of Coös Group, from its admirable development in the northernmost county in the State. The constituents are quartzite, hard and soft mica schist, with or without staurolite, argillitic and calcareous schist, the whole series being nearly 10,000 feet thick. The quartzite is sup- posed to lie at the foot of the system. It covers a large area in Walpole, and in smaller patches is found in all the towns adjoining Connecticut river. Unconformities between the quartzite and gneiss are very marked, particularly in Surry, Keene and Winchester. In Chesterfield and Hinsdale is another conical mountain, over 1,200 feet high, Mt. Wantastiquet, com- posed of argillaceous and mica schists. There are two others in the vicinity nearly as high, Daniels and Barrett's, which connect Wantastiquet with the older gneissic elevations of Winchester. The calciferous mica schist group is very sparingly represented about Drewsville. There is a possibility that a part or all of the Coös group may belong to the paleozoic system. A fossilif- erous limestone, the upper Helderberg, is located immediately adjacent to similar rocks a short distance over the line in Bernardston, Mass. Whatever their age, they are certainly the newest rocks in the Connecticut Valley.
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