bearing on Theoretical Speculations. 195 



be seen in all the pits of Woolwich, Charlton, Chislehurst, and 

 Bexley. It is distinguished from the overlying superficial 

 gravel, by its containing the shells, &c. of the plastic clay. 

 The upper surface of the chalk, wherever it can be examined, 

 appears to have been deeply eroded by the currents which 

 produced this gravel. 



4. I cannot better describe the most recent accumulations 

 of gravel, &c., than by abridging Brongniart's excellent article 

 on the " Terrains Clysmiens ou Diluviens," in his Tableau, 

 p. 66, &c. ; and I am happy to join to my own arguments the 

 views of a geologist so superior. " These deposits," he says, 

 " are the most superficial of all the rocks of the period imme- 

 diately preceding the actual epoch : to the common characters 

 which belong to all the formations of alluvial origin (such as are 

 actually proceeding) they join the peculiar feature of present- 

 ing themselves under circumstances which must oblige us, of 

 necessity, to admit great differences, both as to the forms and 

 elevations of the surface of the earth at the period of their 

 deposition from the actual state, and also as to the mass and 

 force of the aqueous currents which then prevailed. Sometimes 

 these characters are found in their position, for they present 

 themselves at elevations or distances whither no water-course 

 moved by the actual forces, even the most violent, could ever 

 possibly arrive. 



" Sometimes these are distinguished from all actual alluvial 

 deposits by the volume and nature of the fragments which 

 compose them ; for they are often of such a volume, that no 

 actual water-course could possibly transport them, and of such 

 a nature, that they cannot be attributed to the rocks of the 

 soil where they are found ; but must have been detached from 

 rocks so distant, that they must have been transported by a 

 force, of which, in the actual state of nature, no examples are 

 known, that can fairly bear an application to the objects and 

 localities under observation. 



" The organic remains, such as elephants, hippopotami, &c., 

 and the absence of all remains of man and his arts, offer an- 

 other ground of distinction." 



I would only add to these extracts from Brongniart, whose 

 whole article is well worthy of examination by all who wish 

 fully to understand the subject, a few arguments drawn from 

 particular examples. 



I have often been truly curious to know whether the writers 

 who ascribe these diluvial phaenomena to the actual operations 

 of atmospheric waters draining off the surface of the earth, 

 ever could have attempted to present to their minds any thing 

 like a precise view of the districts in question, and of the phae- 



2 C 2 nomena 



