256 GEOLOGY OF OLD HAMPSHIRE COUNTY, MASS. 



1S70. Prof. C H. Hitchcock classes the argilUte as Upper Silurian, and 

 the Bernardston series is "doubtfully referred to the Devonian." "Both 

 above and below are quartzites not of great thickness, and also slates." 

 (13, p. 4.) 



1873. Prof J. D. Dana pronounced the argillite to be an older formation 

 lying unconformably below the other members of the series, as supposed by 

 E. Hitchcock in 1833 for the argillite in relation to the limestone — an 

 opinion receded from on the discovery of an upper band of slate — and by 

 C. H. Hitchcock in 1861 for the overlying quartzite. From the close 

 resemblance of the mica-schist and quartzite on the other side of the Fall 

 River Valley to that on the Williams farm, he assigns to the age of the 

 Helderberg these and the new rocks associated with them, viz, staurolite, 

 mica-schist, hornblende rock, and feldspathic quartzite, which comes at last 

 closely to resemble true gneiss. 



He concluded that the Coos group of Professor Hitchcock, if correctly 

 traced out, was the continuation northward across New^ Hampshire of the 

 Helderberg rocks, and that the two bands of hornblende rocks marked 

 upon Prof E. Hitchcock's geological map of Massachusetts as extending 

 across the latter State, with their continuation southward in Connecticut, 

 as described by Percival, where they pass beneath the New Red sandstone 

 near Middletown, and emerge again w^est of New Haven, were possibly to 

 be assigned to the same horizon. 



1877. In 1877 Professor Hitchcock, first in abstract in the American 

 Journal (16), and later in the Geology of New Hampshire (17), gave the 

 result of a new investigation of the region in question, Avhich diverges in 

 a remarkable degree from his own and his father's conclusions and from 

 those of Professor Dana. Accepting the conclusion of the latter that the 

 argillite is an older and unconformable bed beneath the strata in question, 

 he claims that the limestone "does not cei-tainly dip beneath the quartzite," 

 but. "may be a remnant of a once extensive deposit covering both the 

 other formations mentioned, and what remains is in an inverted position," 

 and thus is newer than all the other rocks of the region. This decided 

 change of opinion caused a discrepancy in the volume already cited, as, in 

 the earlier part, the series is stated to consist of several thousand feet of 

 quartzite, limestones, schists, etc., and probably hornblende-schists. (17, 

 p. 18.) 



