366 Mr. J. Croll on Geological Time, and the probable 



lies buried in the deep recesses of the ocean will escape com- 

 plete disintegration and appear imbedded in those formations. 

 It is only those objects which lie in our existing sea-bottoms that 

 will remain as monuments of the glacial epoch of the Postter- 

 tiary period. And, besides, it will only be those portions of the 

 sea-bottoms that may happen to be upraised into dry land that will 

 be available to the geologist of future ages. The point to be deter- 

 mined now is this : — Is it probable that the geologist of the future 

 will find in the rocks formed out of the now existing sea-bottoms more 

 evidence of a glacial epoch during Posttertiary times than we now 

 do of one during the Miocene, the Eocene, or the Permian period ? 

 Unless this can be proved to be the case, we have no ground 

 whatever to conclude that the cold periods of the Miocene, 

 Eocene, and Permian periods were not as severe as that of the 

 glacial epoch. This is evident; for the only relics which now re- 

 main of the glacial epochs of those periods are simply what hap- 

 pened to be protected in the then existing sea-bottoms. Every 

 vestige that lay on the land would in all probability be destroyed 

 by subaerial agency and earned into the sea in a sedimentary 

 form. But before we can determine whether or not there is 

 more evidence of the glacial epoch in our now existing sea- 

 bottoms than there is of former glacial epochs in the stratified 

 rocks (which are in reality the sea-bottoms belonging to ancient 

 epochs), we must first ascertain what is the nature of those marks 

 of glaciation which are to be found in a sea-bottom. 



We know that the rocky face of the country was ground down 

 and striated during the glacial epoch ; and this is now generally 

 believed to have been done by land-ice. But we have no direct 

 evidence that the floor of the ocean, beyond where it may have 

 been covered with land- ice, was striated. Beyond the limits of 

 the land-ice it could be striated only by means of icebergs. But 

 do icebergs striate the rocky bed of the ocean ? Are they adapted 

 for such work ? It seems to be almost universally assumed that 

 they are. But I have been totally unable to find any rational 

 grounds for such a belief. Clean ice can have but little or no 

 erosive power, and never could scratch a rock. To do this it must 

 have grinding materials in the form of sand, mud, or stones. 

 But the bottoms of icebergs are devoid of all such materials. 

 Icebergs carry the grinding materials on their backs, not on 

 their bottoms. No doubt, when the iceberg is launched into the 

 deep, great masses of sand, mud, and stones will be adhering to 

 its bottom. But no sooner is the berg immersed, than a melt- 

 ing process commences at its sides and lower surface in contact 

 with the water ; and the consequence is, the materials adhering 

 to the lower surface soon drop off and sink to the bottom of the 

 sea. The iceberg, divested of these materials, can now do very 



