208 Frank Carney 



of the earth. The extensive continental glaciers of the Quater- 

 nary fitted well into the early idea of earth-origin. 



To day it is generally accepted that our rock horizons show 

 four distinct glacial periods. The earliest, and the only one which 

 is not as yet fortified by data convincing to all students, is connec- 

 ted with the Proterozoic period. The next belongs to the Cam- 

 brian, then the Permian, and finally the Pleistocene, the most 

 recent period. 



Evidences of earlier glacial periods. Metamorphosed glacial 

 products become clastic rocks. Glacial gravels and sands, when 

 indurated, can not always be distinguished from similar sediments 

 of non-glacial origin ; but glacial conglomerates usually have dis- 

 tinctive features. The heterogeneity of this conglomerate usualh' 

 distinguishes it from any other clastic rock that is catalogued as 

 a conglomerate. Whereas it is possible to find in rivers conglom- 

 erate stones that have been striated while they were held fast in 

 floating blocks of ice and came in contact with other rock, yet such 

 striated bowlders are very rare. Consequently, a conglomerate 

 rock which contains many polished and scratched bowlders is of 

 glacial origin. Furthermore, the matrix of glacial conglomerate, 

 containing, as it does, a large percentage of bowlder clay, has dis- 

 tinctive features, which are obvious when examined in thin sec- 

 tions under a microscope. While a widespread conglomerate, 

 with numerous striated bowlders in a matrix of glacial clay, is 

 good proof of a glacial period, at the same time, to remove the 

 matter entirely from doubt, such a conglomerate, locally at least, 

 should overlie scored, grooved, or striated rock surfaces; glacia- 

 tion is the only agency that is known to thus alter rock surface. 

 These two lines of evidence make the definition of a remote gla- 

 cial period conclusive. 



Proterozoic glaciation. Of these earlier glacial invasions, the 

 evidences supporting this one has only recently been published. 

 In Canada, in the vicinity of Sudbury, Professor Coleman of 

 Toronto, over two years ago, studied a conglomerate rock, which 

 he interprets as glacial in origin. His later reports array proof 

 which has been accepted by many other geologists. Field work 

 has not yet shown how extensive this conglomerate is. It should 

 be remembered that, according to current ideas, our continent was 

 very small during the Proterozoic period ; also, that the rocks then 

 in existence have suffered much from weathering and erosion 



