22 Dr. G. J. Hinde — On a Neio Fossil Sponge. 



ice there to expand more than the colder ice overlying, and therefore 

 to move in the direction of least resistance. That direction of least 

 resistance must, under these circumstances, usually remain near the 

 bottoms of the valleys, and it must tend to be modified (1) by the 

 form of the surface adjoining; (2) by the position of the main 

 feeders of that particular ice-stream ; and (3) by the situation of the 

 terminal portions of the glacial stream itself. 



Another factor comes in here. The movement of a thick mass of 

 ice under enormous pressure (25 tons per square foot for every 

 thousand feet of thickness of ice) must result in the conversion of 

 part of the force so exerted into heat. This in its turn brings 

 about a still further expansion of the parts of the ice in direct 

 contact with the rock, and thus contributes still further to the 

 erosion that is being accomplished by these means. Indeed, it 

 appears to me more than likely that, when once the movement of 

 the lower strata of the ice is set up, terrestrial radiation on the 

 one hand, and the heat generated by the enormous friction on the 

 other, tend to impel the sole of the ice forward with much more 

 regularity, and with much greater evenness of motion, than can be 

 shown to obtain in any part of the surface of any glacier that has 

 yet been carefully examined. 



It appears to me that this view of the causes that determine the 

 flow of land-ice will enable us readily to understand the origin of 

 many phenomena of denudation which northern field-geologists 

 have long agreed to refer to glacial action, although no one has 

 explained satisfactorily how those results were accomplished. Lake 

 basins ; the remarkable terraces and scars of Wensleydale, etc. ; the 

 corries or coums so characteristic of glaciated districts ; the great 

 glacial ruts so well seen near AjDpleby, for example, or near 

 Edinburgh, can each and all be readily enough accounted for if we 

 extend M. Brunner's observations to their proper conclusion, and 

 assume that the flow of a large mass of land-ice is not limited to 

 its upper parts, but extends also to the bottom layers in contact 

 %ith the rock. 



IV. — Notes on a New Fossil Sponge from the Utica Shale 

 Formation (Ordovician) at Ottawa, Canada. 



By George Jennings Hinde, Ph.D., F.G.S. 



ME. H. M. AMI, F.G.S., of the Geological Survey of Canada, 

 who has devoted special attention to the fauna of the Utica 

 Shale in the neighbourhood of Ottawa, lately sent me for examination 

 several fragments of slabs of this rock containing some peculiar 

 sponge remains, which seem to me to be worthy of notice, although, 

 from their mode of preservation, no decisive determination as to the 

 character of the sponge to which they belong can be arrived at. 



The fossils in question appear to the naked eye as so many 

 circular, or, in some instances, fan-shaped, faintly-marked rusty 

 patches on the surface of the black shale, each consisting of delicate 



