446 GEOLOGY OF OLD HAMPSHIEE COUTTY, MASS. 



THE HOLYOKE SHEET. 



Situated a few miles below College Hill, Mouut Holyoke has been for 

 many years annually visited by me with my classes, and has been also 

 assigned, part by part, to small groups of advanced students for their first 

 essays in practical geological work. Many men who have devoted their 

 lives to geology were of especial assistance to me in making out the struc- 

 ture of this rugged and heavily wooded area.^ 



The o-reat sheet of diabase which makes tlu-ough most of its length 

 the crest of the Holyoke range is a contemporaneous flow resting upon the 

 coarse granitic sandstone, which it bakes, and it is covered by exactly 

 similar coarse, light-liuff sandstone. (See PI. IX.) 



In the eastern end of the range the bluffs which overhang the Belcher- 

 town ponds contain no trap, and one must skirt the sandstone ridge for a 

 long distance westward before coming to the first outcrop of the volcanic 

 rock. This emerges from the sands of the post-Grlacial lake (in the roadside 

 just east of H. and L. E. Upham's house) midway on the north slope of 

 the ridge. 



Curiously, this eastern end of the sheet, where it disappears beneath 

 the sands, is dii-ected northeast, while the south end of the great Deerfield 

 bed in Mount Toby is directed southeast, toward the great core of diabase 



' In 1894 Mr. Benjamin Smith Lyman published, in an article entitled " Some New Red horizons " 

 (Proc. Am. Pbilos. Soc, Vol. XXXIII, p. 192), "a conjectural map of the Connecticut and Massachu- 

 setts N'ew Red." This map is said to have been "compiled from Professor Emerson's map of the Massa- 

 chusetts New Red," so far as the part here under discussion is concerned. On the same page (loc. cit., 

 p. 202) it is stated that "the topography seemed to indicate clearly thi' necessity of reducing the 

 extent of the trap, in some places very much," and " in Massachusetts, too, near Mount Toby, and at 

 the eastern end of Mount Holyoke, the topography seemed to require the changes that have been 

 made in the mapping of the trap." As a result, the trap is carried along the bare sandstone ridges to 

 the Belchertowu ponds and apparently doubled in a wholly inaccurate way, while the Deertield bed is 

 still more wrongly drawn. The whole shows clearly the incapacity of the gentleman to interpret 

 topography in terms of geology. Again, the coarse conglomerates of Mount Toby, which my map 

 shows to rest on all sides directly on the crystallines, is assigned to the "Gwynnedd shales" and jilaced 

 in the upper half of the series above the "Xorristown shahs," to which a thickness of G.IOOJ- feet is 

 assigned. All the fossils of the Trias are referred in an indefinite way to the "Norristown shales" — 

 that is, to a horizon below the Mount Toby conglomerates, which is also wide of the facts. At the 

 beginning of the article, in the midst of several pages of harsh criticism of his predecessors, the 

 author says of his attempt, "There is reason to hope that it may keep well within the not wholly 

 unprecedented New Red proportions of 2 bushels of conjecture to 2 grains of fully ascertained fact." 

 (Loc. cit., p. 193.) So far as Massachusetts is concerned, I think he has hardly kept within the pro- 

 portions he had set himself, and this is the moie surprising as the author is a native and nominal 

 resident of Northampton, which is in sight of the rooks he has mapped so incorrectly. 



