408 PEOCEEDINGS OF THE GEOLOGICAL SOCIETY. [JuilO 19, 



exhibit no connexion with the cnrvilinear or arc-disturbances before 

 referred to, but associate themselves in more than one way with 

 those upcasts of similar character which have accompanied the 

 elevation of other Chalk districts, such as the Hog's Back and Ports- 

 down Hill. There is, however, evidence, in the position occupied 

 by the Thames gravel on the south of the Thames, that a line of recti- 

 linear disturbance, although long subsequent to the formation of the 

 original valleys in this part by the arc-disturbances and by denuda- 

 tion, preceded the introduction of that gravel and brought up the Lower 

 Tertiary beds between Woolwich and Erith along a straight east-and- 

 west line, against which the gravel-waters on their south shore rested. 

 It seems to have been the oscillations to which these preliminary dis- 

 turbances gave rise that, in the Thames-gravel channel at least, intro- 

 duced the waters from which that formation was deposited, because 

 we have evidence, in the presence of a fluviatile formation beneath the 

 Thames gravel, much more limited in extent than the latter, that the 

 trough had in this part been evacuated by the sea, and then reoccu- 

 pied by it during a partial submergence which introduced the gravel- 

 waters far above the northern edge of the previous fluviatile deposit. 

 The underlying fluviatile deposit is a brick-earth, which has in some 

 parts, with the gravel, been elevated into high terraces, and in other 

 parts left, also with the gravel, but little disturbed. As Mr. Daw- 

 kins has asserted, in his late paper upon the Brick-earths of the 

 Thames valley, that there is no distinction between this deposit and 

 that of Grays, which belongs to the newer fluviatile series, or that 

 occupying a lower terrace than the Thames gravel and formed 

 after its break-up, I subjoin a section in proof of the contrary, 

 the point involving the important question whether or not much 

 of the Thames gravel was introduced over a Postglacial land-sur- 

 face. On the south side of Dartford Heath this oldest brick-earth 

 (x 4') may be seen coming out inland from under the gravel, the two 

 in superposition being exposed in the subway of Hulsewood House, 

 while by Hill House, near the 101-feet altitude-mark on the west 

 of Dartford, and upwards of 80 feet above the Cray and Darent 

 gravels, I saw 12 feet of the deposit pierced to the chalk. 



This oldest brick-earth {x 4'), by reason of its great and unequal 

 thickness, descends at Erith nearly to the river, towards which it 

 occupies the same apparent position as the Grays bed ; but along the 

 line of the section fig. 12 (as well as along other lines of section 

 given in the memoir) it is cat down by a very sharp denudation, 

 some 50 or 60 feet, to the gravels of the Cray and Darent and of 

 the lower terrace, which have an extensive spread on either side of 

 Grays, and underlie the lower portion of the hrick-earth of that place y 

 being worked in the fields after the brick-earth has been removed. 



The organic remains yielded by the two brick-earths being appa- 

 rently that upon which Mr. Dawldns has based his opinion (for he 

 has given no structural sections in support of it), may not differ; 

 but the physical evidence indicates their separation by an interval 

 adequate to the deposition of a slowly formed gravel of far -travelled 

 material 20 feet thick, and of a brick-earth (from 6 to 8 feet thick) 



