and on the Fossil Remains contained in them. 143 



also the remains of land animals in Essex occur a little be- 

 low the surface, in a line with the marshes, which are a 

 very few feet above high-water mark. By a communication 

 of the late Mr. William Trimmer of Kew, it appeared that 

 he found, under the sandy gravel, a bed of earth, highly 

 calcareous, from one foot to nine feet in thickness; beneath 

 this a bed of gravel a few ftet thick, containing water, and 

 then the main stratum of blue chiy. At the bottom of the 

 sandy gravel, he observed that the bones of the luppopnta- 

 mus, deer, and elephant were met with ; but not in those 

 parts of the field to which the calcareous bed did not extend. 

 Here also a considerable number of small and apparently 

 fresh-water shells, and at the bottom snail -shells, were 

 found. Does it not stem that the first appearance, or crea- 

 tion, of land-animals was on the dry land of this stratum, 

 and that they were overwhelmed in these spots by that sea 

 which deposited the present superincumbent strata of gravel? 



STRATA INTERPOSED BETWEEN THE CLAY AND THE 

 CHALK. 



It is almost impossible to speak with precision of tlie 

 subjacent strata, which are situated between the ciay and 

 the chalk, since very considerable variations occur as to their 

 thickness, and indeed as to the form in which their consti- 

 tuent parts are disposed ; and since there exist but few sec- 

 tions, at least in the neighbourhood of the metropolis, which 

 present a view of the strata composing this formation. They 

 are included in the following account bv Mr. Farey : '* A 

 sand stratum, of very variable thickness, next succeeds, and 

 lays immediately upon the chalk, in most instances, as 

 between Greenwich and Woolwich, on the banks of the 

 Thames; which has oFten been called the Blackheatksand: 

 it frequently has a bed of cherty sandstone in it, called the 

 gray- weathers*." 



On the upper part of a mound at New Charlton some 

 traces ot the lowest part of the blue clay appear, covered by 

 not more than a foot of vegetable earth. This layer of clay 

 does not seem to exceed two feet in thickness, which, in- 

 deed, it possesses only on the top of some of those mounds, 

 which occur so frequently as to render the surface in this 

 district very irregular. In this clay, oysters of different 

 forms are found ; some approaching to the recent species, 

 and other* longer and somewhat vaulted : but they are in 

 general so tender as to render it very difficult to obtain a 



• Report on Derbyshire, &c. voL i. p. 111. 



tolerable 



