u U^ 



^\ I ^ 



382 



THE AZOIC SYSTEM AND ITS SUBDIVISIONS. 



theoretical grounds. (Canadian Nat, 1878, (2) VIII. pp. 227-240, 



262-278.) 



lit 1876 Mr. D. F. H. Wilkins illustrated in a paper upon Labrador 



some of the methods employed in the study of crystallinq rocks. The 

 supposed formations were determined by lithological characters, the folia- 

 tion taken as the lines of stratification, and an apparent dike regarded a 

 representative of the Norian. He says : '' The stratification lines are 

 very often so obscure that it is almost impossible to say whether the 

 rocks are metamorphic or eruptive" ; and of the Norian at one locality, 

 that it consists of "red-weathering, gray hyperitein abed two feet thick, 

 overlaid by four feet of whitish gneiss . . . ., seen to repose, at low tide, 

 upon the underlying red gneiss of Lower Laurcntiau age." (Canadian 



Nat, 1878, (2) VIIL pp. 87, 88.) 



Thus far we have found no evidence except lithologieal in support of 

 the ages to which the crystalline rocks of Labrador were assigned. 



MAINE. 



The geological survey of Maine, under Prof. Chas. H. Hitchcock, de- 

 veloped nothing of value as determining the question whether the Azoic 

 system existed in that State. No evidence bearing on this question 

 other than lithologicd was furnished. 



Dr. Hunt in his Geognosy of the Appalachians infers from lithologi- 

 eal characters and difference in dip that the '' mica schists and gneisses " 

 are of Montalban age, while the " greenish chloritic and chromiferous 

 schists" in the vicinity of Portland are Huronian and older than the 

 gneisses. (Presidential Address, 1871, p. 10.) 



Prof. Chas. H. Hitchcock objected to the views of Dr. Hunt, holding 

 that, while the rocks in question were Montalban and Huronian, tlio 

 Montalban was the older, and the Huronian at this point was deposited 

 upon it. He states that '* at the line of junction as observed in Dcer- 

 ing, the two groups of rocks possess exactly the same inclination," and 

 declares that, if in their natural position, the gneiss underlies the schist. 

 He acknowledges that the only way these formations have been identi- 

 fied is by lithologieal characters, remarking that 



" Logan, in 1855, described a system of rocks overlying unconforniably the 

 Laurentian gneisses about Lake Huron, which were distinguished by means of 



