Geography of Ohio 209 



during later periods. It i.s possible, therefore, that, an extensive 

 glacial formation of this early period may have been quite largely 

 removed during later time. 



A more interesting fact, however, connected with the Huronian 

 ice age, is the bearing it has on formerly accepted ideas of condi- 

 tions that prevailed immediately preceding the Proterozoic period. 

 The rocks of this early period are sometimes thought of as cooled 

 magmas or congealed liquid material of the parent earth ; and the 

 absence of fossils in these early rocks has been explained by saying 

 that the surface of the earth was then so hot that life could not 

 exist thereon. If glacial conditions existed in a particular part of 

 the Proterozoic continent, it is quite conclusive evidence that 

 there, at least, the surface was not warm. 



Geologists of Norway also report conglomerate, suggesting 

 glacial origin, belonging to rock horizons that appear to correlate 

 with the Huronian of North America. If their correlation is 

 correct, this early period witnessed glaciation in two distant parts 

 of our sphere. 



This early glacial period has a significant bearing on our ideas 

 of the origin of the earth. Such refrigeration could hardly be 

 possible under the nebular hypothesis. It is, however, entirely 

 possible under the planetesimal theory of earth-origin. 



The Cambrian glaciation. In connection with studies carried 

 on in China, under a Carnegie grant, by Bailey Willis and others, 

 a conglomerate horizon of glacial origin was located in the upper 

 Yangtze valley. This horizon contains beautifully striated bowl- 

 ders, as well as other conclusive evidences of glacial origin. Its 

 location in the geologic scale is also made definite by the fact that 

 it immediately overlies a formation whose fauna is well known. 

 Glacial conglomerate of the same age has been identified in south 

 Australia. 



The Permian glaciation. In India, Africa, and Australia the 

 existence of glacial conglomerates belonging to this period has 

 been established. No other pre-Pleistocene glaciation is more 

 thoroughly understood. In south Africa, these conglomerates were 

 pointed out a long time ago, but students were very slow in accept- 

 ing the interpretation. The time correlation of beds in such dis- 

 tant parts is made definite by relationship to other horizons bear- 

 ing well known fossils. In south Africa, the glaciated surfaces 

 underlying these conglomerates are as beautifull}- preserved as 



