MINERALOGY AND GEOLOGY.
Art. I. Remarks on the Geology and Mineralogy of a Section of Massachusetts on Connecticut River.
Art. I. Remarks on the Geology and Mineralogy of a Section of Massachusetts on Connecticut River, with a Part of New-Hampshire and Vermont; by Edward Hitchcock, A. M. Principal of Deerfield Academy.
The geology of this tract, from a few miles south of Northampton in Massachusetts, to the north boundary of Brattleborough in Vermont, and of Chesterfield in New-Hampshire, is shown on the subjoined map. The primitive formation, except the argillite, is coloured vermilion; the secondary, blue; and the alluvial, gamboge yellow, according to Cleaveland. The alluvial part is elevated above the bed of Connecticut river from 10 to 100 feet, and, in most places, reposes on red sandstone. The soil in the northern part is generally argillaceous; but in the southern more siliceous. The secondary formation consists chiefly of detached eminences that rise abruptly from the plain, and are composed of red sandstone and puddingstone alternating, except the elevations A and B, (Holyoke and Tom) and a part of the range CD, passing through Deerfield and Greenfield, which are greenstone. The part coloured rose-red consists of argillite, sometimes alternating with mica slate, siliceous slate, or chlorite slate. It is thus coloured to show the extent of the argillite, and not from a belief that this rock is of the transition class; for in this region the argillite is undoubtedly primitive. Some quarries of this rock have been opened in Massachusetts; and in Vermont are extensively wrought. I have not learnt how far the argillite extends northward in Vermont and New-Hampshire. Its strata are almost perpendicular, inclining a few degrees to the west.
The primitive region on the west side of Connecticut river, included by the map, is made up of mica slate, as a prevailing rock, particularly in the northern part. Hornblende slate sometimes alternates with this, and sienite appears in various places, though its strata are generally thin. Limestone also occurs in Deerfield, Conway, Colrain, &c. of a dull brown colour. It contains so large a proportion of silex that it is often but little removed from granular quartz. Lime for building has sometimes been obtained from it. A range of granite, containing veins of lead ore, appears at Southampton, and proceeds to Hatfield. North of this, the other rocks cover it, and it does not again rise within the limits of the map.
Sienite is the prevailing rock on the east side of Connecticut river in the primitive region, more particularly in the southern part. In some places a narrow stratum of mica slate lies next to the conglomerate of the secondary formation, and a low range of graphic and common granite has been observed in Amherst and Leverett, lying next to the mica slate. Other veins of granite also traverse the sienite; and gneiss occurs in many places. The proportion of hornblende in the sienite is generally small, and mica is often present in considerable proportion. Porphyritic sienite is common in this quarter, and steatite occurs in its eastern part.
Most of the primitive region on the map is broken and mountainous, being made up of parallel ridges and detached eminences. The strata run nearly north and south, and dip to the east at angles between 20° and 60°. It would be easy to extend the map on the west to the top of Hoosack mountain, since the country is all primitive; and on the east the primitive continues, with a few exceptions, to the ocean. The map might also be extended to the boundary of Connecticut, by prolonging the primitive ranges with some divergency, and colouring the intermediate space secondary, except a narrow tract on the east side of Connecticut river, which is alluvial. These extensions were not thought necessary.