xxxvi GENERAL SUMMARY OF SCIENTIFIC AND 



old sea-limits, spread its limestones not only over the Chazy, 

 Calciferous, and Potsdam (which in some parts of New York 

 it overlies unconformably), but over the surrounding more 

 ancient crystalline rocks, and extended far over these to the 

 northward of Lake Ontario and up the valley of the Sag- 

 uenay. As regards the relations of these formations of the 

 first and second faunas in the valleys of Lake Champlain and 

 the St. Lawrence, they were supposed by Logan to be due 

 to movements which succeeded the deposition of the latter ; 

 but according to Hunt we must admit that the principal 

 movements were anterior, and that the rocks of the second 

 fauna rest unconformably on those of the first. 



Further contributions to our knowledge of the fauna of 

 these older rocks, as seen in the valleys just named, have been 

 made by Billings and by Ford. Hunt has lately pointed out 

 that we can not, with correctness, apply the name of Silurian 

 to these rocks, which correspond to the Middle and Lower 

 Cambrian of Sedgwick, and to the first palaeozoic fauna of 

 Barrande. He therefore proposes to retain for these the name 

 of Cambrian, in which the Quebec group, and the Potsdam 

 and Calciferous, and perhaps the Chazy of the New York se- 

 ries, are to be included. The rocks of the second fauna the 

 Cincinnati group, which represent what was originally the 

 debated ground between Sedgwick and Murchison he pro- 

 poses to call Siluro-Cambrian, reserving, with Sedgwick and 

 Rogers, the name of Silurian for the rocks of the third fauna 

 only. In this he is but returning to the old distinctions es- 

 tablished by Hall and Rogers in their comparisons of Amer- 

 ican and British rocks, in conformity with the results of Sedg- 

 wick, Salter, and others, which were, without good reason, set 

 aside by Murchison and his followers. The whole subject 

 will be found in Hunt's recently published "Essay on the 

 History of Cambrian and Silurian." In it he has moreover 

 given a concise notice of the Cambrian fauna of our eastern 

 sea-coast as seen in Massachusetts, New Brunswick, and New- 

 foundland ; and he agrees with Hartt, Dawson, and Selwyn 

 in referring to this horizon the gold-bearing rocks of Nova 

 Scotia. In this connection he has discussed again the age 

 of the crystalline rocks of New England, and, in opposition 

 to the former generally received view, maintains that these 

 are all pre-Cambrian, and assigns the Green Mountains to the 



