GEOLOGY OF THE CONNECTICUT VALLEY DISTRICT, 34I 



group of the Vermont report, and Upper Silurian (supposed Niagara) of 

 Sir W. E. Logan's report, — and separated by a distance of one hundred 

 and sixty-five miles. The mica schist is probably an older formation 

 than the Helderberg, lying in a trough of clay slates, the latter consti- 

 tuting the floor of the fossiliferous beds. These slates may be Cambrian, 

 judging from general considerations. No fossils yet appear in them. 

 The calcareous schists carry a few obscure crinoidal fragments at Derby, 

 Vt., which are of no value in the identification of strata. 



At first sight, one would declare that there is no similarity between 

 the Littleton and Bernardston rocks. After considerable study of both 

 localities, I find a few points of resemblance, perhaps as much as we 

 have a right to expect in synchronous deposits more than a hundred 

 miles apart. In our studies we often look for exact resemblances in re- 

 mote localities. Perhaps it is better that the connecting tie be discov- 

 ered with difificulty, in which case the conclusions may be more surely 

 established. The surroundings at Littleton are different from those at 

 Bernardston. The series rests on diorites and diabases, close by gneiss 

 and argillitic quartzites at Littleton. At Bernardston, the underlying as 

 well as the overlying rock is quartzite ; and in the neighborhood are the 

 mica and staurolite schists denominated in my report as the "Coos 

 group." Prof. Dana thinks it clear that the Massachusetts Helderberg 

 and the Coos group, as defined by me in reports of 1869 and 1870, are, 

 "if correctly traced out," identical. 



Inasmuch as the limestones in all these localities are characterized by 

 a similar large crinoid, those at Bernardston and North Lisbon contain- 

 ing no other form whatever, and occur in the same open valley of the 

 Connecticut, it is presumable they are of the same age, and that is the 

 Silurian Helderberg, as made known by the presence of Halysites and 

 Pentaincnts. The opinion of Prof. James Hall, to the effect that the 

 crinoids in the Bernardston limestone are like those of the Onondaga or 

 Upper Helderberg limestone of New York, has been quoted.* Since 

 that time I understand that similar fossils have been found much lower 

 down, so that they were not necessarily confined to the Onondaga. The 

 correlation of the Massachusetts and New Hampshire limestones is bet- 

 ter, using the same fossil for our guide, since the localities are contiguous 



* Proc. Avter. Ass. Adv. Sci., vol. vi, p. 300, 



