234 THE GLACIAL OR ICE EPOCH. 



has not been determined, but that a similar declension took 

 place in those areas is sufficiently obvious from a similar 

 change in their flora and fauna.* That the pre- glacial 

 land was somewhat higher than the present is shown 

 by old river-courses and land -surfaces that lie below the 

 existing sea-level, as well as by ice-marked rocks that dip 

 away beneath the waters. Had the pre-glacial lands been 

 lower, these rock -surfaces would not have been smoothed 

 and furrowed by ice, nor would the old land-surfaces have 

 made their appearance, t It was on this more elevated 

 surface, therefore, that the glacier and ice-sheet first began 

 their operations ; and it is at this stage that we find the 

 lowest tenacious clays ("lower till"), and angular blocks 

 and boulders, little removed from the rocks from which they 

 were severed. Here, then, we have the first stage of the 

 glacial epoch the operation of ice on a land-surface some- 

 what more elevated, in its average altitude at least, than the 

 existing continents of Europe, Asia, and North America. 

 This operation, as we have learned from the preceding 

 Sketch, must have been to grind and gouge in the valleys, 

 to smooth and round the higher eminences, and generally 

 to polish the harder rocks the detritus or abraded mate- 

 rial being carried forward to lower levels, there to be laid 



* According to Professor Dana, there are no tertiary strata in North 

 America to the north of the New England States, the northern area having 

 been dry land while the southern was under water and received the ter- 

 tiary deposits. To this elevation of the northern lands, and the subse- 

 quent gradual uprise of the southern or tertiary portion to the height of 

 3000 or 5000 feet, he attributes the first setting-in of the glacial epoch. 



t The attention of geologists has not been sufficiently directed to these 

 pre-glacial land-surfaces. It is true that the "lower till" rests for the 

 most part on abraded rock-surfaces, but there are many localities (we have 

 noticed them in Kincardine, Ayr, Fife, and Durham to say nothing of 

 the well-known Cromer beds in Norfolk) where it reposes on sands, 

 gravels, and even peaty beds, which were undoubtedly the soils and river- 

 gravels of the period immediately preceding ; and in these we may expect 

 to find the remains of the true pre-glacial flora and fauna. 



