232 ME. W. HILL OK THE BEDS BETWEEN THE 



18. On the Beds between the Uppee and Lowee Chalk of Doyee, and 

 their comparison with the Middle Chalk of Cambeidgeshiee. By 

 William Hill, Esq., F.G.S. (Eead February 10, 1886.) 



Introductory. 



I PEOPOSE in the following paper to give a description of certain beds 

 lying between the Upper and Lower Chalk of Dover, and to compare 

 them with those described as '•' Middle Chalk " by Messrs. Penning 

 and Jukes-Browne in the " Geology of the Neighbourhood of Cam- 

 bridge," a memoir of the Geological Survey. 



The chalk of the area described in this memoir is divided into 

 Lower, Middle, and Upper, and the authors say (on p. 20) that 

 these divisions are founded on the combined evidence of the litho- 

 logical and palaeontological characters of the strata. They describe 

 the divisions as separated by bands of chalk having marked litho- 

 logical characters : that separating the Lower from the Middle 

 Chalk is a hard nodular rock, spoken of as coinciding with a palae- 

 ontological break, and is called Melbourn Hock : that separating the 

 Middle from the Upper Chalk is the band of crystalline chalk, long 

 ago brought to the notice of geologists by Mr. Whitaker, E.G.S., and 

 known as the Chalk Mock*. 



These two bands, the authors continue, form such marked breaks 

 that the chalk falls naturally into the divisions of Lower, Middle, 

 and Upper ; and these exactly correspond with the palaeontological 

 zones, Cenomanian, Turonian^ and Senonian, established by Dr. 

 Barrels and Prof. Hebert in the north of Prance. 



Still referring to the Survey memoir, the Middle Chalk is (at 

 p. 21) divided into four zones, viz. : — Melbourn Bock, as its base ; 

 zone of Rhynchonella Cuvieri, 60 feet ; zone of Terebratulina gracilis, 

 in two divisions, upper and lower, 150 feet ; and on the top, the 

 Chalk Bock. 



Pinally, with reference to the Chalk Bock the authors say (p. 22) : — 

 " Its fauna, which is worthy of detailed investigation, appears to 

 contain a mixture of Middle- and Upper-Chalk forms, together 

 with some that may be peculiar ; amongst these last are several 

 Gasteropods." 



Since the memoir was written, Mr. Jukes-Browne and myself 

 have recognized, not only in the area included in the memoir, but 

 also through the counties of Hertfordshire, Bedfordshire, Bucking- 

 hamshire, and Oxfordshire, a zone of Belemnitella 'plena. This 

 zone, which consists of inconstant bands of marly and rocky chalk, 

 formerly included in the Melbourn Bock, forms the summit of the 

 Lower Chalk. 



General Description of the Chalk of Dover. 

 The lower part of the chalk between Folkestone and Dover has 



* Quart. Journ, Geol, Soc. vol. xxi. p. 398, and Geol. Surv. vol. iv. p. 46. 



