340 On the Absence of any Traces of the fall of Aerolites. 



be admitted, that as yet there is no satisfactory proof of the 

 fall of aerolites on the earth's surface prior to its last modifica- 

 tion, or to the glacial period. 



Let us now refer to my second subject, namely, the absence 

 of any traces of glacial action in the ancient strata. Here it 

 is only necessary to observe, that one effect of glacial action, 

 namely, the transport of large angular fragments of rock by 

 floating ice, is still exhibited to us by the regular progression 

 of large masses of polar ice loaded with fragments of rocks 

 from the arctic towards the tropical regions; and there cannot 

 be a doubt that many such blocks of large size must be every 

 year dropped by the melting ice on the bottom of the ocean. 

 From the greater extension of glaciers, which also still exist on 

 the mountains, in the epoch preceding the present, it has been 

 reasonably inferred that all glacial phenomena were in like 

 manner more extended ; and a sufficient cause has been thus 

 acquired, in the floating ice of that epoch, for the production of 

 the effects exhibited in many of our gravel beds, and in the 

 remarkable phenomenon of the huge angular erratics scattered 

 over the surface, irrespectively of the nature of the rock on 

 which they rest. But when we pass this boundary, our evi- 

 dence fails us; and although in the vicinity of a basaltic flow 

 lumps of that subaqueous lava may be occasionally found im- 

 bedded in the strata close to it, or at the very base of the cliff 

 where it was forming, some large fragments of rock may be 

 found in a sandstone or conglomerate; the general character 

 of the secondary formations is not such as to warrant us in 

 concluding that ice had co-operated in their production, whilst 

 the absence of ' erratics ' or large angular blocks in such for- 

 mations is a strong negative proof that ice did not then exist. 

 Is not then this curious negative fact a remarkable confirma- 

 tion of the positive evidence afforded by organic remains, that 

 prior to the glacial period the whole earth enjoyed a tempe- 

 rature in some measure assimilated to that of its now tropical 

 regions? It is true that in the more recent tertiary formations 

 there is an approximation to the now existing conditions as 

 to temperature ; but it was only an approximation, and widely 

 different in degree from that extraordinary state of depressed 

 temperature which followed in the glacial period. It may then 

 be asked, can the extraordinary change which produced the 

 glacial period be explained or its cause assigned ? and, in like 

 manner, can the resumption of a comparatively genial tempe- 

 rature by the earth's surface be explained ? Few philosophers, 

 I believe, are satisfied by the explanation, however ingenious, 

 of such changes, as given by Mr. Lyell, having been produced 

 by alterations of the relative position of sea and land ; and most 

 philosophers look beyond the globe, and seek in great astrono- 





