THE GLACIAL OK ICE EPOCH. 



THE GLACIAL EPOCH AS DISTINGUISHED FROM THE PRE - GLACIAL 

 OR LATER TERTIARY ITS BOULDER-CLAYS, GRAVEL-DRIFTS, AND 

 ERRATIC BLOCKS LIMIT OF THESE IN THE NORTHERN HEMISPHERE 

 CONDITIONS UNDER WHICH THEY APPEAR TO HAVE BEEN FORM- 

 ED ICE-MANTLE, GLACIERS, AND ICEBERGS DURATION OF THE 

 PERIOD PAUCITY OF LIFE DEPRESSION AND RE -ELEVATION OF 

 LAND GRADUAL RETURN OF MORE GENIAL CONDITIONS ESTAB- 

 LISHMENT OF EXISTING ARRANGEMENTS, PHYSICAL AND VITAL 

 RECURRENCE OF COLDER AND WARMER CYCLES IN TIME. 



THERE are few chapters in geological history possessed of 

 more interest than that which is usually known as the Gla- 

 cial Epoch, and none that has received a larger share of 

 attention from modern investigators. Indeed, it is still to a 

 great extent an unsolved problem, and hence the conflicting 

 views that prevail as to the physical conditions of the period, 

 and the causes by which these conditions were produced. 

 Though beset with many difficulties, the general features of 

 the period are well known, and it is to place these broadly 

 before the general reader, rather than enter upon debatable 

 hypotheses, that we attempt the present Sketch. 



As mentioned in a preceding paper, the genial tempera- 

 ture that prevailed during the deposition of the earlier ter- 

 tiaries began gradually to decline during the middle and 

 later portions, till towards the close of the period an intense 

 cold set in, and ice seems to have prevailed alike over the 

 land and waters. Of course, we refer more especially to the 



