On the Beds between the Upper and Lower Chalk of Dover, and their comparison with the Middle Chalk of Cambridgeshire

Abstract

Introductory . I propose 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 Cambridge,” 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 lithelogical and palaentological characters of the strata. They describe the divisions as separated by bands of chalk having marked lithelogical characters: that separating the Lower from the Middle Chalk is a hard nodular rock, spoken of as coinciding with a palmontological break, and is called Melbourn Rock : 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, F.G.S., and known as the Chalk Rock . 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 palaeontologicalzones, Cenomanian, Turonian , and Senonian , established by Dr. Barrois and Prof. Hdbert in the north of France Still referring to the Survey memoir, the Middle Chalk is (at p. 21) divided into four zones, viz.:― Melbourn Rock , as its base; zone of Rhynchonella Cuvieri , 60 feet ; zone of Terebratulina gracilis , in two divisions, upper and lower, 150 feet;