TALCHEEB COAL FIELD. 49 



The question naturally, indeed inevitably, suggests itself — How these 



The "boulder bed" enormous blocks of stone, manifestly requiring a 



how produced. ^^^^ f^j.^^ ^^ ^l^jg^^jg ^^^ transport them, are 



found mixed with a sediment so fine, that in any, except a very sluggish 

 current, it must have been swept away, and could not have been deposited ? 

 It seems difficult, in so hot a coimtry, to conceive what yet appears 

 to be the only probable explanation of this phenomenon, which indicates 

 that the boulders must have been conveyed hither by some floating 

 substance and deposited among a very fine sediment which was at the 

 time in course of deposition by a very sluggish current. It is true 

 indeed that, in some Mountain Lakes (e. g. that of Geneva), a fine sedi- 

 ment may be brought in and deposited by one tributary stream, while 

 boulders of considerable size are being swept down by another ; but 

 besides the extremely local nature of all such deposits, the very 

 conditions of their deposition would seem to prevent their forming any 

 one bed like that which we are considering. 



Should any evidence hereafter accrue, allowing the inference that these 



beds may have been formed in a lake, on a 

 Perhaps ground-ice. 



high table land, where the winter temperature 



was sufficiently low to admit of ice reaching the waters of the lake 



without melting, then an adequate explanation of the phenomenon may 



be given, as it resembles exactly the effects of the action of gTound-ice, 



which, enabling boulders to be carried down by a sluggish current, would 



undoubtedly produce such an intermixture of large rounded masses 



of rock and of fine silt, as is seen in the present case.* 



Possibly a more minute examination of the boulders may reveal 



groovings and scratchings on their surfaces. The presence of these, 



however, on the supposition of ground-ice having been the means of 



transport, should not by any means be looked for with certainty, and 



• Lyell's Priaoiples, 1853, p. 219, and De la Beohe's Geological Objjerver, p. 212-3, 



H 



