NATURAL HISTORY OF CREATION. 51 



they form a necessary first link in the chain of nutrition ; 

 but their not being found first, is no proof that animals 

 of any kind existed before them, seeing that, however 

 abundantly they might be developed, their forms and 

 substance were too slight to have a chance of being pre- 

 served with any distinctness amidst rocks which appear 

 to have undergone a considerable degree of heat. And 

 the same cause, it is obvious, would prevent our having 

 any memorial of the very lowest forms of animal life. 



The exact point in the ascending stratified series at 

 which the first traces of organic life are to be found is 

 not clearly determined. Dr. M'Culloch states that he 

 found fossil orthocerata (a kind of shell-fish) so early as 

 the gneiss tract of Loch Eribol, in Sutherland; but 

 Messrs. Sedgwick and Murchison, on a subsequent 

 search, could not verify the discovery. It has also been 

 stated, that the gneiss and mica tract of Bohemia con- 

 tains some seams of grauwacke, in which are organic re- 

 mains ; but British geologists have not as yet attached 

 much importance to this statement. We have to look 

 a little higher in the series for indubitable traces of 

 organic life. 



AI10V0 the gneiss and mica slate system, or group of 

 strata, is the Clay Slate and Grauicacke Slate System; 

 that is to say, it is higher in the order of siiprajmsit'wn, 

 though very often it rests immediately on the primitive 

 granite. The sub-groups of this system are in the follow- 

 ing succession upwards: — i, hornblende slate; 2, chiast- 

 olite slate ; 3, clay slate ; 4, Snow don rocks (grauwacke 

 and conglomerates) ; 5, Bala limestone; 6, Plynlymmon 

 rocks (grauwacke and grauwacke slates, with beds of con- 

 glomerates). This system is largely developed in the west 

 and north of England, and it has been well examined, 

 partly because some of the slate beds are extensively 



