lil Mr Murchison on the Glacial Theory. 



ward persistent march (iu many parts up-hill) of a body of glaciers, har« 

 ing a front of many hundred miles in extent, is irreconcileable with any 

 imaginable subaerial action. On the other hand, it was proved, by the 

 presence of sea shells of an arctic character, that the " terra firma" to 

 which some of the blocks had been transported, had been the bed of the 

 Northern or glacial Sea at the period of this transport. We then at' 

 tempted to explain how the parallel striae and polishing of the surface of 

 rocks of unequal altitude was reconcileable with the submarine action of 

 ice, by supposing that the ice floes and their detritus might be set in mo- 

 tion by the elevation of the Scandinavian continent, and the consequent 

 breaking up of great glaciers on the northern shores of a sea which then 

 covered all the flat regions of Russia ; and we further stated our belief, 

 that the bottoms of these icebergs, extending to great depths, must have 

 ever}' here and there stranded upon the highest and most uneven points 

 of the bottom of the sea into which they floated j that where the bottom 

 was hard rock, the lower surface of the iceberg, like the lower surface 

 of a glacier, would grate along and score and polish the subjacent mass ; 

 that where the bottom consisted of tenacious mud or clay, the iceberg 

 once fairly stranded would be retained till it melted awaj', entirely or in 

 part, whilst it would be more frequently borne over sand-banks, on ac* 

 count of their less resistance. In this manner, we endeavoured to eiQ' 

 plain not only the scratches and polish of hard submarine rocks, but also 

 why large blocks are often found on former submarine hills, and why (in 

 Hussia at least) such blocks are more frequently associated with clay 

 -than sand. These views were indeed first expressed at the Glasgow 

 meeting of the British Association, when I strove to reduce a large por- 

 tion of the Alpine glacial theory to considerations depending upon the 

 fact, that during the eera of the dispersion of the large blocks, by far the 

 greater portion of our continents were beneath the sea, 



Mr Maclaren, to whom I have already adverted, has recently improved 

 this view, by shewing how the parallel scratches and grooves ranging from 

 ■N.NW. to S.SE., and the dispersion of blocks in that direction, are re- 

 concileable with the union of currents from the N., set in action, as above 

 supposed, by a great polar elevation which acted as a " centre of disper- 

 sion ;" but, as the author adds, a broad current would also set continually 

 eastward along the immersed regions included in the temperate zone ; 

 «,nd hence, he says, that when the icebergs were drifting southwards 

 from the poles, they would naturally be carried to the SE. by a stream 

 compounded of the two currents. After reasoning upon the wide appli- 

 cation to which the view of floating iceberg action is capable, and how 

 many of our present terrestrial appearances it will explain, Mr Maclaren 

 •adds, *^Mr Murchison's hypothesis, if adopted, does not exclude that of 

 •Agassiz. On the contrary, it may be assumed, that while the glacial 

 condition (which caused the great accumulation of ice in the northern 

 regions) continued, every mountain chain, which then had an elevatien 

 of 2000 or 3000 feet above the sea, would be encrusted with ice, perhaps 



