276 ANNUAL OF SCIENTIFIC DISCOVERY. 



Sillery sandstone, the whole, from the base of the conglomerate, having 

 a thickness of about seven thousand feet. These red and green shales 

 resemble closely those at the top of the Hudson River group, and the 

 succeeding sandstones are so much like those of the Oneida and Me- 

 dina formations, that the Quebec group was for a long time regarded 

 as belonging to the summit of the Lower Silurian series, the more so 

 as, by a great break and upthrow to the south-cast, the rocks of this 

 group are made to overlap the Hudson River formation. This great 

 dislocation is traceable in a gently curving line from near Lake 

 Champlain to Quebec, passing just north of the fortress ; thence it 

 traverses the island of Orleans, leaving a band of higher strata on 

 the northern part of the island, and after passing under the waters of 

 the gulf, again appears on the main land about eighty miles from the 

 extremity of Gaspe, where, on the north side of the break, we have, 

 as in the island of Orleans, a band of Utica or Hudson River strata. 

 By a detail of evidence too voluminous to be presented in this arti- 

 cle, Mr. Hunt next shows that this Quebec group is simply the greatly 

 developed representative of the New York Potsdam and calciferous 

 sandstones; that it is identical with the " Taconic system" of Ern- 

 mons, and tlie true base of the Silurian system in America. He also 

 considers that the liypozoic series of rocks described by Prof. H. D. 

 Rogers as underlying the Silurian formation in Pennsylvania, the 

 Green Mountain yneissic formation, and a series of limestones, sand- 

 stones and conglomerates in Tennessee, first described by Mr. Saf- 

 ford, and designated by him as Cambrian, are really equivalents of 

 this Quebec group more or less metamorphosed. 



METAMORPHISM OF CONGLOMERATES INTO GNEISS, TALCOSE 



SCHISTS, ETC. 



In the May number of Sillimari's Journal (1861), Prof. Edward 

 Hitchcock re-discusses the subject * of the origin of the curious elon- 

 gated, curved, and flattened quartz pebbles, which are especially no- 

 ticeable in the conglomerates of Newport, R. I., and also at various 

 localities in Vermont, and contributes much additional information 

 to our knowledge of the phenomena in question. 



Professor Hitchcock's conclusions respecting the elongated pebbles 

 of Newport are as follows : 



1. This rock was once a conglomerate of the usual character, ex- 

 cept in the great abundance of the pebbles, and it has subsequently 

 experienced great metamorphoses, making the cement crystalline and 

 schistose, and elongating and flattening the pebbles. 2. The pebbles 

 must have been in a state more or less plastic, when they are elon- 

 gated, flattened, and bent. If their shape has been thus altered, 

 their plasticity must of course be admitted ; for the attempt to change 

 their present form would result only in fracture and comminution. 

 The degree of plasticity however must have varied considerably; 

 for some of them are scarcely flattened or elongated at all, and, as 

 has been stated, some arc not cut off by the joints. 



i For a previous discussion of this subject, see Annual of ScL Dis., 1861, pp. 

 282, 283, 2 



