RASAY. GEOLOGY. 251 



forms the bulk of the island. Together with this shale, 

 there are very thin beds of limestone ; very impure, 

 inasmuch as they contain clay, sand, and mica, by .which 

 they are gradually confounded with it until they entirely 

 disappear. The shale also, gradually losing its charac- 

 ter, passes first into a schistose sandstone of an argillo- 

 calcareous composition, and ultimately into the white 

 sandstone. 



The organic remains found in the inferior strata of shale 

 and limestone, are limited both in quantity and in variety ; 

 but they are most abundant in the former rock, and 

 increase in both respects as we follow the beds upwards. 

 The lowest of these fossil substances are a gryphite, a 

 pecten, and a terebratula; the upper are far more numerous, 

 and I shall here subjoin a list of them as far as it was 

 possible to ascertain their characters from the specimens 

 which I procured, often very mutilated and obscure. 1 * It 

 requires a fortunate concurrence of wind and weather to 



* Ammonitae. 



Pectines, some of them resembling those found near Bath and in 

 Gloucestershire others apparently unknown to all our conchologists. 



Terebratulas, smooth and subovate; also, plaited: neither of them 

 definable. 



Ostreae ? the resemblance considerable, though even the genus cannot 

 be decidedly pronounced on. 



Chamas fragments of shells apparently of this genus. 



Belemnitae. 



Gryphites. 



A Cardium ? 



Shells resembling the genus Corbula. 



Ossicula of a star fish or pentacrinites. 



An unknown shell with a general resemblance to Alcyonium. 



Fragments of bivalves resembling a Mya. 



A shell resembling the pecten concentrica of Oxfordshire, but longer 

 its genus not to be ascertained. 



Besides these there are numerous other fragments, but the whole are 

 in so imperfect a state as to be incapable of examination, although they 

 resemble generally those found in the lias of Somerset and Gloucester- 

 shire. 



