29 



LOWER AND UPPER SILURIAN FORMA- 

 TIONSFIRST FORMS OF LIFE. 



THE first leaves of the Stone Book have been damaged by 

 fire. It is acknowledged by all geologists that the rocks of 

 what has been called the Gneiss and Mica Slate System, were, 

 subsequently to their deposition, exposed to so high a tempera- 

 ture, that, though organic remains had been entombed in them, 

 we should have had no chance of seeing these preserved. ( n ) 

 If it be a fact, therefore, that no distinct traces of plants and 

 animals are presented in these rocks, it is no conclusive proof 

 that such did not then exist. But no such fact can be said to 

 have been ascertained. Certain fragments resembling the 

 cases of infusoria (shelled animalcules) have been observed.( 12 ) 

 A few patches of limestone (primary limestone) indicate 

 organic life as having been present where they were formed ;( 13 ) 

 and a similar inference has been drawn from certain experi- 

 ments of M. Braconnot, in which he detected ammoniacal 

 products from masses of this formation. From analogy, 

 moreover, seeing that all other sedimentary formations con- 

 tain remains of living beings it appears, a priori, unlikely 

 that this should be, any otherwise than apparently, devoid of 

 them. ( 14 ) However all this may be, it is certain that the 

 next formation the Silurian is the first in which we find 

 incontestable monuments of the early life of our planet. 



The Silurian System is so named, because a district in 

 western England, where it is largely presented at the surface, 

 and where it was first thoroughly examined, was that occu- 



