Correspondence — Mr. S. V. Wood,jun. 187 



denuded and furnishing erratics, during tlie deposition of the whole 

 Salt Eange series ; and further, that towards the later period (if not 

 before) glacial conditions of the granitic region enabled masses of 

 this rock to be floated to the Salt Eange area by the agency of ice ; 

 there to undergo, in varying degrees, the usual operations of atmo- 

 spheric denudation. A. B. Wynne. 

 Camp Hazara, January 1, 1878. 



ME. S. V. WOOD, Jtjn., IN REPLY TO DE. JAMES GEIKIE. 

 Sir, — Mr. James Geikie has not in his article in your last Number 

 put the questions in issue between us so incisively as I could have 

 wished. 



1. I have never denied that land-ice erodes more in some places 

 than it does in others. What I say is that if the great basin of the 

 St. Lawrence has been eroded by this agency, all land surfaces must 

 have perished in the process. 



2. I have never denied that some moraine accumulates beneath 

 ice. What I say is that nearly all of it travels out to the ice 

 termination. If it does not, how can valleys and basins be eroded 

 by ice ? If the bulk of what is degraded remains beneath the ice, 

 no basin can result ; for the moraine would to the same extent 

 supply the place of the rocks degraded. It is only near the termi- 

 nation of the glacier that any considerable quantity of the moraine 

 accumulates beneath the ice. This (as distinguished from the first 

 accumulated portion of it, which resting on the middle glacial for 

 the most part, though not always, was formed by the dropping of 

 the moraine from floe-ice) I consider to have been the origin of that 

 later part of the chalky clay which covers Lincolnshire, Huntingdon- 

 shire, Cambridgeshire, and the adjoining district, accumulated in this 

 way when the glacier which I have described as coming southwards 

 over Lincolnshire terminated in the sea some twenty or thirty miles 

 west of the Fen boundary ; as well as of that which forms the 

 basement clay of Holderness, which accumulated from an arm of 

 this glacier that came through the Humber. All this moraine, as I 

 hope some day to show in detail, was, except in two or three limited 

 spots, left beneath the sea as the ice wasted away. The part iu 

 Holderness being followed by the depression northwards which 

 brought over the Shap blocks, was succeeded 2minterruptedly by 

 another deposit of material from a different source, the purple clay ; 

 while the rest being in shallow water emerged before any such new 

 deposit could form over it. 



3. Mr. Geikie speaks thus of sands escaping the action of the 

 overriding ice, viz. : " Where the gradually decreasing ice-sheet 

 crawled slowly to its termination, we discover considerable accumu- 

 lations of Till, resting upon apparently undisturbed beds of gravel, 

 sand, and clay " ; and again he says, " That an ice-sheet does under 

 certain conditions ride over incoherent deposits of gravel, sand, silt, 

 clay, and peat without entirely obliterating them." 



Possibly the latter of these two statements may to some extent be 



