42 EXPLANATIONS. 



masses of these earlier rocks gave ammoniacal 

 and combustible products, likewise indicative of 

 the presence of organic matter : in the same sub- 

 silurian region, " fragments, apparently organic, 

 and resembling cases of infusoria," have been 

 detected,* and in Bohemia actual fossils have been 

 announced. Even dubious traces of life in sub- 

 silurian rocks must be admitted to be of import- 

 ance, when we consider that they have mostly 

 been subjected to such a degree of heat as could 

 not fail to obliterate organic memorials, seeing 

 that it has even changed the texture of the rocks 

 themselves. From what Mr, Lyell saw of the 

 Silurian rocks in America, he finds himself called 

 upon, in the most emphatic manner, to warn geo- 

 logists against " the hasty assumption, that in any 

 of these sections toe have positively arrived at the 

 loioest stratum containing organic remains in the crust 

 of the earth, or have discovered the first living beings 

 ivhich were imbedded in sediment.''^ 



" A geologist," he says, " whose observations 

 had been confined to Switzerland, might imagine 

 that the coal measures were the most ancient of 

 the fossiliferous series. When he extended his 

 investigations to Scotland, he might modify his 

 * Ansted's Geology, ii. 60. 



