].88 DEIFT-DEPOSITS OP THE N.W., MIDLAND, AND EASTEEN COUNTIES. 



clay of the north-west could be correlated, and seemed inclined to 

 the opinion that the Hessle clay of Holderness might represent the 

 upper clay of the north-west, as both were characterized by grey or 

 ash-coloured vertical fractures. But I was not then aware of the 

 southerly extension of the upper clay of the north-west, or of its 

 extreme range of altitude, which reaches quite 600 ft. in a typical 

 form, and probably from 700 to 800 ft. in a degenerate and attenuated 

 form. The question remains as to the age of a great sheet of 

 chalkless clay which Mr. Wood lately found extending northward 

 from York through Durham (Geol. Mag. for Jan. 1878). Should 

 this clay prove to be of Hessle age, the Hessle clay might then be 

 regarded as extending from the Wash* to the river Tyne, and 

 therefore more likely to be the equivalent of the upper clay of the 

 north-west than if it had been entirely limited to Holderness and 

 the immediate neighbourhood. 



Note. — In this paper I have made very little reference to the 

 evidence of the relative age of deposits furnished by Mollusca, 

 because I do not consider it in all cases reliable. Mr. S. Y. Wood, 

 Jun., F.G.S., believed that the lower brown clay of the north-west 

 could not be older than the upper part of the purple clay (above the 

 chalky clay) of the Yorkshire coast ; but he relied on shells found 

 in intercalations of sand, consisting of a m^re streak at Dimlington, 

 and at Bridlington of a very limited bed in the midst of large 

 boulders, the latter suggesting the possible flotation by ice of the 

 shell-bearing sand from an older deposit. 



* See Mr. Jukes-Browne's paper on the Southerly Extension of Hessle 

 Boulder-clay in Lincolnshire, Quart. Journ. Geol. Soc. for August 1879. 



