428 NATURAL SCIENCE. Dec. 



for in mental coin, the price is raised and more demanded. Granted 

 the subsidence, another difficulty looms ahead, it must have been 

 differential, and it is pretty positively asserted that no evidence of any 

 kind exists of subsidence south of the British Channel. Also, if there 

 had been differential subsidence and elevation, faults of glacial date 

 might be looked for in the solid crust, whereas there are none. 



These objections as a whole are considered by some geologists 

 serious enough to warrant the introduction of an agent to account for 

 them, of which, unfortunately, we have very little knowledge. This 

 agent is land-ice, and to Greenland we are asked to project our mental 

 vision that we may understand the Glacial Period. I am now neither 

 denying nor affirming the former existence, or probable former exis- 

 tence, of an icy covering to our isles such as is predicated. If, instead 

 of the theoretical possibilities of such a tremendous agent as is postu- 

 lated being dwelt upon, we were treated to actual facts drawn from 

 the investigation of the Greenland ice-sheet, some of us would have 

 a more comfortable assurance of being on solid ground forming a base 

 for the reasoning process. Unfortunately, in the absence of recorded 

 observations, we have to fall back on theoretical considerations alone. 

 I trust it will not be considered arbitrary, when dealing with an agent 

 possessing such potency for work of varied kinds as is claimed for an 

 ice-sheet, to ask for the fullest proof of its powers. Formerly the 

 proof of the action of land-ice was looked for in the local nature of the 

 materials of the Boulder Clay, which represented the ground-moraine, 

 together with the preponderance of planed and striated stones. Now 

 everything in the Drift — foreign rocks, shells, local materials, rounded 

 pebbles and boulders, sea-sands, are all claimed as the effect of land- 

 ice, whether found on the top of a mountain or in the bottom 

 of a valley. 



There is a system of land-ice physics worked up with astonishing 

 ingenuity and skill by which all these puzzling phenomena are 

 theoretically, if we admit the premises, fully explained. If delicate 

 shells are found intact in the Drift at an inland locality such as Gloppa, 

 forty miles from the sea, it is suggested that they have been conveyed 

 over hill and dale simply frozen in the sole of the glacier, forgetful of 

 the fact that the generally comminuted condition of the Drift shells 

 had previously been claimed as a proof of the passage of land-ice 

 across a sea bed. Other materials, such as foreign rocks, have been 

 conveyed in the heart of the glacier, and the whole — rocks, sea-sand, 

 shells have been washed out, rounded and deposited in stratified 

 masses on the sudden melting of the ice which is supposed to have 

 occurred at the close of the Glacial Period. Unfortunately, no instances 

 are quoted of any analogous kind of work performed by existing 

 glaciers or ice-sheets. It is of this dearth of examples that geologists 

 accustomed to the methods of investigation pursued by Hutton and 

 Lyell have a legitimate right to complain. We should all be glad to 

 assent to these various propositions if adequate proof were forth- 



