458 SKETCH TOWARDS A 



that lias been said, of the ocean, or of any limited seas, 

 than either this vacillation, or that filling up of basins 

 and straits, through alluvial deposits, which affects 

 the former, under obvious causes, and, the latter, under 

 the consequences of tide currents. I will here add, 

 that the alluvia of disintegration, of previous condi- 

 tions of the earth, explain the local conglomerates ; as 

 the general ones find their explanation in those of a 

 more general nature, terrestrial or marine, tumultuary 

 or otherwise. 



The last alluvial deposits consist in the agricultural 

 soil, and in peat. The former is the produce of the 

 gradual decomposition of rocks and fragments : it is 

 transported, universally, by means of rain simply ; par- 

 tially, but more rapidly, by rivers ; and it becomes 

 mixed with decomposed vegetable matter. The latter 

 consists of this vegetable matter alone, which I have 

 shown to be a hydrocarbonaceous compound, produced 

 by the action of water, and resembling that which is 

 formed by a close or modified heat ; not being bitumi- 

 nous, but finally becoming so, and thus producing lig- 

 nite, first, as it is also the preparation for future coal. 

 And it is formed under the sea and on its margins, 

 under lakes and on their shores, in marshes, and 'on 

 ill-drained places or declivities ; as it is, further, the 

 produce of fallen forests, and is also occasionally trans- 

 ported, in a powdery state, by the flow of water. Oc- 

 cupying distinct deposits, or strata, it may also alter- 

 nate with alluvial earthy ones, and further, with 

 shells, or marl ; thus representing the successions in 

 a coal field. I have only to add, respecting two very 

 partial alluvia, that I can discover nothing in those of 

 the Caves and the Fissures, justifying the hypotheses 

 on those subjects, or requiring any but the most ob- 

 vious explanations. 



