MODE XIV. SILICEOUS GLUTENITE. 



height above the sea, and said to be eight leagues 

 in circumference, which consists entirely of roll- 

 ed pebbles, and among them some of pudding- 

 stone, probably original, disposed in regular 

 layers, and imbedded in a calcareous cement. 

 The pudding rocks around the great lake Baikal, 

 in the centre of Asia, present the same phe- 

 nomenon ; but it has not been observed whether 

 the fragments be of an original or derivative 

 rock. The derivative are supposed by theorists 

 to have proceeded from vast currents, flowing 

 from the primitive mountains, as on the dimi- 

 nution of the primitive waters these mountains 

 first appeared in the shape of islands, while the 

 remaining parts of continents required many 

 ages before they emerged from the ocean. It is 

 remarkable that this corresponds with the most 

 ancient ideas ; for the Argonauts are represented 

 as sailing from the Euxine Sea to the British 

 Ocean ; and Cesar describes Britain as an island 

 shared between land and water, the rivers being, 

 as in most countries newly inhabited, of enor- 

 mous size. 



The siliceous sand- stones form another im- Sand-stones. 

 portant division of this mode. They may some- 

 times, as already mentioned, be confounded with 

 granular quartz, which must be regarded as a 

 primary crystallisation. The sand, which has 



VOL. L, Q, 



