73 



thick, which consists of alternating layers of limestone and 

 gneiss singularly corrugated, lying between masses of evenly 

 laminated hornblendic gneiss"*. The latter, from its structure, 

 may be regarded as due to sedimentation but the corrugation 

 of the enclosed " layers of limestone and gneiss " is totally 

 inconsistent with its being of similar origin. Obviously the 

 phenomenon is an example of segregated lamination, whose 

 corrugation is the effect of internal movements, in individual 

 beds, produced by chemical forces, 



The latest estimate of the thickness of the entire group of 

 Archaean rocks has been made by Mr. Henry G . Vennor, who, 

 from very careful and laborious observations carried on during 

 a number of years, is entitled to the highest confidence, and 

 " from whose views " Mr. Alfred R. C. Selwyn, Director of the 

 Canadian Survey, says " he has no reason to dissent." " It 

 would appear that the whole volume is not less than between 

 50,000 and 60,000 feet ; and this estimate does not include the 

 great fundamental unstratified or obscurely stratified gneisso- 

 syenitic series, but commences only with the first strata of 

 clearly stratified gneiss." As to the great fundamental series, 

 it is at present impossible to suggest even its approximate thick- 

 ness ; but, forming the backbone of Eastern Ontario, as well as 

 thousands of square miles in the region to the northward of the 

 Ottawa river, it ' ' is apparently a distinct formation, though the 

 separation between it and the first strata of the overlying stra- 

 tified gneiss is not always clear "f- 



It is well known that the late Sir William Logan designated 

 the great metamorphic group under consideration by the name 

 Laurentian, also adding thereto, with a distinctive title, another 

 metamorphic group, on the whole mineralogically different, which 

 he regarded as an unconformably overlying one. But the inves- 

 tigations of Vennor have thrown some doubt on the alleged 

 unconformity ; the latter geologist is nevertheless disposed to 



* Geology of Canada, 1863, p. 27. Dr. Bigsby, speaking of the bands of 

 Canadian crystalline limestone, states " they are tortuous, and often, by bend- 

 ing round, sharply return by a parallel course to within a short distance from 

 their visible point of departure. Corrugated seams of gneiss are sometimes 

 enclosed in the limestones" (Geological Magazine, vol. i. p. 156). 



t Report of the Geological Survey of Canada for 1876 and 1877, pp. 280, 

 299 ; 300. 



