Geology. 9 



ton, and part of the Croydon areas) was unacquainted with the 

 existence of any Chalk in this district higher than the MICRASTER 

 COR-ANGUINUM zone. 



Owing to an accident last year his work of exploration was 

 hindered, but now the Congress may be congratulated that, owing 

 to having selected Woolwich as their centre this year, the writer, 

 in order to give an accurate description, has recently visited new 

 localities for the express purpose of examining the Chalk immedi- 

 ately underlying the Tertiaries or in their near neighbourhood, 

 and has discovered, for the first time, the zone of UINTACRINUS in 

 this district. 



Turning to our southern boundary, we have at Keston the 

 same zone as at Charlton, Wickham, Abbey Wood, and Dartford ; 

 that of MICRASTER COR-ANGUINUM. 



At Orpington, in a field to the north-east of the Church, there 

 is a small exposure about 30 feet long and about 12 feet deep, 

 showing a very soft and creamy white chalk almost destitute of 

 flints which has yielded the UINTACRINUS plates and ossicles 

 previously mentioned. Associated with these the writer found 

 MICRASTER COR-ANGUINUM and a portion of ACTINOCAMAX VERUS. 

 At Foots Cray there is a large pit on the Farningham Road in the 

 MICRASTER COR-ANGUINUM Chalk. 



The Chalk underlying the Thanet Sand at Dartford, and in the 

 neighbourhood, has been repeatedly examined by the writer and 

 by Mr. Sherborn, but has yielded no indication of a higher zone 

 than that of MICRASTER COR-ANGUINUM. 



Continuing south towards the escarpment (with which tract, 

 however, we are not specially concerned), the succeeding lower 

 zones are met with, and shown in the railway-cuttings and large 

 pits at Poll Hill (Dunton Green) and Otford, where formerly large 

 lime-works existed in the HOLASTER SUBGLOBOSUS zone (Lower 

 Chalk). The Darent at this point has carved its course through 

 the zone of HOLASTER SUBGLOBOSUS, the ACTINOCAMAX PLENA 

 Marls, and the following zones of the Middle Chalk : RHYNCHO- 



NELLA CUVIERI, TEREBRATULINA GRACILIS, HOLASTER PLANUS, and 



MICRASTER COR-TESTUDINARIUM. This last being succeeded b}^ 

 the Micraster cor-anguinum and Uintacrinus zones of the Upper 

 Chalk, the lithological character of which differs from that of the 

 lower beds, the latter being harder, nodular, frequently gritty, and 

 below the T. gracilis zone, destitute of flints. On the other hand, 

 flints are abundant in the Upper Chalk, except in the Uintacrinus 

 :zone. The chalk of both the uppermost zones is very soft and 

 easily worked ; so that the removal of the matrix from the fossils 

 is easy, and this frequently suggests the zone. 



