Ch. XIV.] THE GLACIAL PERIOD. 265 



within the tropics, in the southern hemisphere Professor 

 Hartt has found glacial drift extending from Patagonia, 

 all through Brazil to Pernambuco, and Agassiz has even 

 announced the discovery of glacial moraines up to the 

 equator. I have myself seen, near Pernambuco, and in 

 the province of Maranham, in Brazil, a great drift 

 deposit that I believe to be of glacial origin ; and I 

 think it highly probable that the evidence that is accu- 

 mulating will force geologists to the conclusion that the 

 ice of the glacial period was not only more extensive 

 than has been generally supposed, but that it existed at 

 the same time in the northern and southern hemi- 

 spheres, leaving, at least, on the American continent, 

 only the lower lands of the tropics free from the icy 



covering. 



I shall not enter upon the question of the cause of the 

 cold of the glacial period. It is probably closely con- 

 nected with the cause of an exactly opposite state of 

 things, the heat of the miocene period, when the beech, 

 the hazel, and the plane, lived and flourished in Spitz- 

 bergen, as far north as latitude 78, and, according to 

 Heer, firs and poplars reached to the North Pole, if 

 there was then land there for them to grow upon. I 

 consider that the great extension of the ice in the 

 glacial period supports the conclusion of Professor 

 Heer, founded on the northern extension of the miocene 

 flora, that these enormous changes of climate cannot be 

 explained by any rearrangement of the relative positions 

 of land and water, and that " we are face to face with a 

 problem whose solution must be attempted and doubtless 

 completed by the astronomer." 



There is another branch of the subject that I can- 



