1 



by the passage over them of Sharp Detrital Matter. 121 



deposits only in connection with, and as illustrated by, the 

 phenomena of Alpine glaciers." On a former occasion I 

 stated, as Sir R. Murchison has also done, that the composi- 

 tion of our apcient conglomerates and sandstones is, from the 

 absence of boulders, such as not to lead to a belief that even 

 glacial or ice action had existence at the time of their deposit ; 

 and if this opinion be correct, accumulations of ancient drift 

 in sand, gravel, and mud must have then taken place through 

 the agencies of fluviatile and marine currents alone. But let 

 me ask, has the recent removal of any of the secondary or 

 tertiary strata from the rocks below them, either by quarry- 

 ing or fluviatile action, laid bare surfaces worn in the manner 

 which has been described ? I have seen evidences thus dis- 

 played of the ordinary action of water, but I have not seen 

 the polished or striated surfaces. Often, for example, may 

 be seen on the sloping side of the beds, the surface of mica- 

 ceous schist, when recently bared by the removal of super- 

 ficial strata, still exhibiting the well-known ripple marks, 

 but no transverse striae or grooves. I throw out this observa- 

 tion in the hope that the absolute antiquity of such markings 

 may be defined. "Whilst, however, I cannot limit the pheno- 

 mena of drift to any one glacial cause, I must admit and 

 acknowledge the vast importance of the recent study of glacier 

 action, as without the demonstration of the more extended 

 existence of ancient glaciers it would be impossible to satisfy 

 the mind that a truly glacial epoch had occurred in the earth's 

 history. The establishment of the former extension of glaciers 

 naturally proves the greater amount of general cold, and 

 prepares us to admit the floating icebergs and icefloes, which 

 are assuredly the most natural and efficient means of trans- 

 porting the huge erratic boulders which have been spread 

 over our now dry land. Such phenomena are now exhibited 

 by the icebergs of our own seas, which convey fragments of 

 rock thousands of miles from their natural seat ; and would 

 it not be truly unphilosophical to deny the possibility of such 

 agencies at more remote epochs, or to refuse the corroborative 

 evidence which ancient glacier action adduces in its support. 

 But whilst the glacier and the iceberg were performing their 

 parts, the river and the seas were not idle ; and thus the true 



