334 THE REVOLUTIONS OF THE CRUST OF THE EARTH. 



transportation been accomplished by water, shells would be found in the 

 drift, which is not the case. 



The members of the geological commission of Canada* have found 

 many transported blocks both in the mountains and in the valleys of 

 this province. The blocks of each locality consist of a mixture of 

 different rocks, although one of local or distant origin strongly predomi- 

 nates over the others. In almost every case the blocks seem to have 

 been transported toward the south." There are some signal excep- 

 tions, however. Thus, in the county of Runouski, in the valley of the 

 river Neigette, there are several calcareous bowlders transported from a 

 distance of several miles in an opposite direction from the ordinary, 

 that is, to the northeast. Dr. Dawson has observed similar instances in 

 Nova Scotia. This phenomenon is not confined to the northern heini- 

 sphere.t Darwin discovered the existence of similar blocks in South 

 America, and almost within the same limits, that is to say, about 50° 10' 

 of south latitude. About the seventy-second degree of west longitude 

 these boulders are very numerous. They consist of feldspathic rocks, 

 of the schists, chlorites, quartzes, and the basaltic lavas. This phe- 

 nomenon, then, is very general, and consequently every theory which 

 attempts to explain it by any local cause must be discarded. In pro- 

 portion as we approach the tropical regions the phenomenon gradually 

 disappears, and no trace of it is found beyond the forty- fifth degree of 

 latitude north or south. It is, therefore, almost impossible to suppose 

 that the bowlders of one hemisphere were carried into the other, and 

 consequently it must be admitted that this phenomenon occurred peri- 

 odically upon each of the two hemispheres. 



If we admit that a very general cause must have presided over the 

 dissemination of these transported blocks, still we cannot deny that 

 sometimes a local cause may produce the same phenomenon. North 

 America furnishes an example of this. In Canada the mean tempera- 

 ture of winter is 9° 9', and in Labrador it is still less. The winters 

 there are very rigorous, producing the congelation of the mouths of the 

 river Saint Lawrence, as well as of the rivers which empty into Hud- 

 son's Bay, among others of the Saskatchewan, and the Churchill. As 

 this barrier of ice occurs when the winter rains of the northern part of 

 North America produce great inundations, it is violently broken up, 

 and the ice of the submerged plains is carried away, with everything 

 which has collected upon it. This cause of the dissemination of bowl- 

 ders cannot be generalized, for the simple reason that the periodical 

 rains in Europe do not always occur in winter. 



To explain the phenomena of erratic boulders most scientists have 

 recourse to ice ; and differ only in regard to the cause which could pro- 

 duce an extension of the glaciers. Thus Charpentier supposed that the 



•Report, Montreal, 1864, p, 947. 



Wn the Distribution of Erratic Boulders, etc. Trans. Geolog. Soc, London, 3d 6er. 

 vol. vi, p. 415. 



