OUTLINES OF THE GEOLOGY OF WESTERN MASSACHUSETTS. TOPOGRAPHY. channels deeper. It is obvious that these exist­ details of fact which constitute the record are formations stand in their proper relative positions, ing conditions under which the plain is being described in the essay relating to each quadrangle. the oldest at the bottom. In order to follow this general description, destroyed are not those under which it was The greater portion of the rocks of the Green which is applicable to territory extending beyond formed. Mountains in Massachusetts were once horizontal ALGONKIAN PERIOD. the limits of the Holyoke quadrangle, Quadrangles To gain an idea of the manner of development beds of gravels, sands, clays, and marls, Origin of the In the usage adopted in this atlas the term the reader is referred to the following referred to- of the once level surface of the plateau, we may which became consolidated into con- rocks- "Archean" is applied to those most ancient crys­ topographic sheets of western Massachusetts: conceive the present process of gradual glomerates, sandstones, shales, and limestones. talline rocks which form part of the Greylock, Hawley, Greenfield, Becket, Chester­ wearing down carried to completion. They began to accumulate at a time remote in original crust of the earth and which ancient rocks 0 of this region, field, Northampton, Sandisfield, Granville, and When the streams shall have carved plateau- the geological past, when the region was invaded antedate and underlie the oldest sedi- Springfield, all on a scale of 1 mile to 1 inch. away the elevations now existing, the plateau by the sea. There had been land of an extent mentary rocks. Used in this sense notArchean- The Green Mountain range passes across the and hills will be reduced to a surface of very not now known. It subsided and the sea spread there may not be any Archean rocks in the region. State of Massachusetts, between the valleys of gentle slope, rising gradually from sea level. over it. During the occupation of the The reat The name "Algonkian" is applied to all sedimen­ _ the Connecticut Kiver on the east and Green Moun- Such a plain is called a peneplain, or, when district by the waters, which was pro- tSlgSs- tary rocks up to the base of the Cambrian, which the Housatonic and Hoosic rivers on worn to a uniform surface at the lowest alti­ longed, there were changes in the s!on' rocks are at present without known distinctive the west. It does not here include descriptlon- tude above sea, a base-level. In the course of height of the land and the position of the shore fauna and are usually highly crystalline. The mountains of great height, as in Vermont, but is development of such a peneplain the sea may line about the submerged area, and the sediments Algonkian period, as here used, is therefore equiv­ a broad plateau. On the west it is bounded by encroach upon its area. To the limits of the deposited in the sea varied accordingly. In these alent to the later portion of the Azoic of Lyell, a high, steep, and continuous scarp; on the east encroachment the waves cut away all low hills deposits were doubtless buried, as fossils, some of the Eozoic of Dawson, and the Archaean of Dana. it descends by a more gradual and undulating and fill hollows, producing a plain which is even the early forms of life of the Cambrian and Silu­ Washington gneiss. The oldest rocks of this slope. The western crest has an elevation of more uniform than any stage of the peneplain of rian types. Eruptions of igneous rocks also region appear at the surface in oval areas sur­ about 2000 feet. The surface is deeply cut by erosion, except perhaps the extreme case of a occurred and caused the intercalation of various rounded by younger strata. They have been laid narrow valleys, with a few rounded hills rising base-level. Such a wave-smoothed surface is lavas with the sediments. bare by erosion of the beds which once deeply to inconsiderable heights above the average level. called a plain of marine gradation. In adjustments of the earth's form during sub­ covered them. The line of these ovals extends The western and more elevated portion of this The former plain of the Green Mountain pla­ sequent ages, down to and including south from the Hoosac Tunnel along the crest of , i -< -i i. -i -i ,0. -i . Chemical plateau lies along the eastern edge of Berkshire teau may still be recognized by one who stands the Carboniferous period,L ' the Cambrian changes*** physical of the plateau. The rocks belong to the oldest County and forms part of the Berk- upon its surface and scans the horizontal sky line a^id Silurian rocks were subjected to JTnTsnurian sedimentary system, the Algonkian, . TT'ii -IT /» Berkshire shire Hills, but the greater part of the H'M<*> the which represents it on a level with his position. chemical reactions and to pressures rocks* and are highly crystalline. They ' o J: western por- rocks- upland occupies the western half of It extended evenly westward from the Berkshire sufficiently powerful to disguise or obliterate the consist of firm, coarse gneisses which gne?ssesand 7 ° limestones. Franklin, Hampshire, and Hampden plateau- Hills over the now deep Housatonic-Hoosic Val­ original structure of the rocks. contain minerals and possess structures counties. Its western edge is a continuous ley, to touch the crest lines of the Taconic Moun­ The sheets of sediment changed form in a not formed in the later rocks, and thick beds of divide from which nearly all its drainage is into tains, which lie along the western boundary of manner which can best be compared to the coarse and highly crystalline limestones with the Connecticut. Only at one place, in Hinsdale, Massachusetts. Down this surface flowed the crumpling of sheets of paper. The Chan esof many minerals, some of which are rarely found in does this line of watershed make a large bend to rivers which cut the upper canyon of the West- pressures to which the beds were sub­ later limestones, as chondrodite, wernerite, dark sediment' the east so as to throw a considerable area of field Valley in Washington and the Farmington jected were greatest from east to west. pyroxene and hornblende, and coarsely crystal­ upland drainage to the west into the Housatonic. Valley in Otis. Those who have most carefully They therefore forced the beds into folds running lized graphite. Considerable beds of pyrrhotite, The plateau is traversed in deep and narrow studied the aspects of the plateau are agreed that north and south. The folds developed as alter­ magnetite, and graphite also occur. valleys by the main streams and branches of two it was once a peneplain, worn down by frost, nate arches and troughs; as the compression con­ Because of the presence of these heavy lime­ principal rivers, the Deerfield and the Princi al rains, and streams. They.differ as to what part tinued they were pinched together, so that many stones, which were probably of marine organic Westfield. .The Deerfield River, enter- SKffi marine gradation may have played in modifying of the beds which had previously extended in a origin, we may assume that the whole series, ing from Vermont with a southwest- p a eau* its surface. In any case it formerly extended horizontal attitude came to stand vertical or nearly except possibly the hornblende-gneiss of East Lee, erly course, turns abruptly eastward. At the from the sea by a gentle slope to moderate alti­ so. From such positions they were pressed over was sedimentary, but we know nothing of the bend is now the eastern entrance to the Hoosac tudes. It has been raised to its present elevation westward, overturned, and many of the folds laid in limits of the sea in which the strata were spread. Tunnel. The Agawarn or "Westfield Kiver by earth movements, and these were no doubt as an eastward-sloping attitude. The folds were of CAMBRIAN PERIOD. gathers its waters by three convergent streams : gradual as they were extensive and mighty. various sizes, ranging from microscopic plications the Westfield River, flowing south from near the To follow the history of the landscape of to arches several miles across. In the deeper Becket gneiss and Cheshire quartzite. The valley of the Deerfield ; the Middle Fork of the western Massachusetts still further back into portions of the whole mass the rocks were so rocks of the Algonkian period had grown old; Westfield, flowing south by east; and the West the past, we must appeal to the rocks Landsea es confined, yet forced to move by such pressures, they had assumed a highly crystalline texture, Fork of the Westfield, flowing southeast. The as guides. Their record is transcribed JloScai that they were squeezed and thrust one fold upon had been strongly folded and deeply eroded, and last-named stream rises in a gap in the crest of under the next head, " General geol- perio s* another. Where this occurred on a minute scale, through many ages had stood as dry land, while the plateau edge between Becket and Hinsdale. ogy," but something of it may appropriately be as it did throughout the Green Mountains, the the atmospheric waters had softened and disin­ This gap is in fact a deep canyon, ample for the sketched here. rocks are divided into thin laminae, which some­ tegrated them to a very great depth. Then the occupancy of a considerable river, in the swampy The carving of the old peneplain of the Green times differ from the original layers in the sand land sank and the waters of the Cambrian sea bottom of which the headwaters of the Westfield Mountain plateau occurred during and before the and clay, and are therefore called schists.