ANCIENT GLACIERS IN EASTERN HEMISPHERE. 141 



dicate a greater altitude for the land in pre-glacial times, 

 since a river could not erode its channel to such a depth 

 below sea-level. The argument appears inconclusive for 

 one principal reason : no mention is made of any river 

 gravels or other alluvium in the borings. Indeed, there 

 is an explicit statement that the deposits are all glacial, 

 showing that the channel must have been cleared out by 

 ice. This, therefore, leaves open the vital question, 

 whether the deposits removed were marine or fluviatile. 

 It may be remarked that the great estuary of the Mersey 

 has undoubtedly been produced by a post-glacial (and 

 probably post-Roman) movement of depression. 



" The Pre- Glacial Climate.— In all speculations regard- 

 ing the cause of the Glacial epoch, due account must be 

 taken of the undoubted fact that it came on with extreme 

 slowness and departed with comparative suddenness. In 

 the east of England an almost perfect and uninterrupted 

 sequence of deposits is preserved, extending from the early 

 part of the Pliocene period down to the present day. 



" These in descending order are : 



" 1. Post-glacial sands, gravels, etc. 



" 2. Glacial series. 



" 3. The ' Forest Bed ' and associated marine deposits. 



" 4. Chillesford clay and sand. 



" 5. The many successive stages of the Eed Crag. (The 

 Norwich Crag is a local variation of the upper part of the 

 Red Crag.) 



" 6. The Coralline Crag. 



" The fossils preserved in these deposits, apart from the 

 physical indications, exhibit the climatal changes which 

 accompanied their deposition. The Coralline Crag con- 

 tains a fauna consisting mainly of species which now 

 range to the Mediterranean, many of them being restricted 

 to the warm southern waters. Associated with these are 

 a few boreal forms, but they are represented in general 

 by few individuals. Here and there in the deposits of 



