1853.] TRIMMER ON THE GRAVELS OF KENT, 287 



north and west, with others which I refer to the south ; and as 

 forming an attenuated and modified representative of the Upper 

 Erratic Tertiaries of the counties north of the Thames. 



The cretaceous zone of North Kent will form the subject of a 

 future communication, — " On the Mammalian Deposits of the Valley 

 of the Thames, and their relations to the Erratic Tertiaries and the 

 Warp-drift." 



In the district which I am now describing, there are, at different 

 heights, and of somewhat different composition, three beds of gravel, 

 which would be all comprised in Mr. Martin's tertiary zone. I shall 

 call them the Dartford gravel, the Shooter's Hill gravel, and the 

 Rochester gravel. See Plate XIII., and the Table at the end of this 

 Paper. 



Dartford Gravel. — The Dartford gravel extends through Bexley 

 and Dartford Heaths, and the Common called the Brent, as far as 

 Greenhithe, with a breadth of about a mile, running about half a 

 mile further up the left bank of the Darent, where it extends nearly 

 to the church of Sutton-at-Iione. 



It forms a kind of terrace, about 1.50 feet above the tidal level. It 

 is higher, therefore, than the mammalian deposits of the ancient 

 Tham.es. It is further, also, from the existing stream, and bounds the 

 trough in which the ancient and more extensive river flowed (see PL). 



This gravel has been cut through by the valley of the Darent, and 

 by the minor inosculating valleys, which are destitute of streams. 

 The best sections are in the gravel-pits at Wilmington, by the 

 Orange-tree Turnpike-gate ; also, in a gravel-pit on the opposite or 

 right bank of the Darent, near the Powder Mills ; in a cutting of the 

 North Kent Railway, a little east of the Dartford Station ; also, in an 

 old pit at Sutton Place, and in some of the cuttings on the Rochester 

 road, between Stone and Greenhithe. 



In the Wilmington pit, the maximum depth of the gravel is about 

 15 feet; and though it is impossible to separate this deposit from 

 that at the railway cuttings, which contains a greater variety of frag- 

 mentary rocks, I can find no pebbles here but unabraded and sub- 

 angular flints, rolled eocene pebbles, and fragments of quartzose and 

 cherty sandstone of various colours ; the latter I refer to the strata 

 below the chalk, which are exposed within the area of the Weald. 



At the Powder Mill pit, the materials of which the gravel is com- 

 posed are nearly the same as at Wilmington, consisting of slightly 

 worn flints, some of them of considerable size, eocene pebbles, and 

 the quartzose and cherty sandstone before mentioned as being pro- 

 bably subcretaceovis. 



There are some peculiarities in the mode of aggregation of the 

 gravel at this pit worthy of notice, as indicating violent and conflict- 

 ing currents during its deposition. The section is about 30 yards 

 long ; for about 7 yards at the western end, there are some tolerably 

 regular lines of stratification. These terminate abruptly against one 

 of those unstratified masses of loam and gravel, which in a paper on 

 the " Pipes or Sandgalls in the Chalk of Norfolk^'S" I have described 

 * Quart. Journ. Geol. Soc. vol. i. p. 310. 



