382 THE AZOIC SYSTEM AND ITS SUBDIVISIONS. 



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

 2 G 2-2 78.) 



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

 some of the methods employed in the study of crystalline 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 hyperite in abed two feet thick, 

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

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

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



Thus far we have found no evidence except lithological 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 lithological was furnished. 



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

 cal 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 Hiu-onian, the 

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

 upon it. He states that " at the line of junction as obsei-ved in Deer- 

 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 lithological characters, remarking that 



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

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



