Correspondence, 427 



clay in the coast cliffs. This I admitted in my first paper, and am 

 quite aware it presents di prima facie case in favour of Mr. Wood's views ; 

 and furthermore on the view I suggested I should expect that the 

 variety in the component materials of Mr. Wood's " middle drift " 

 would prevent any certain distinction being observable between 

 them and the gravel seen on the coast, even if a section happened to 

 expose their junction. 



The difficulty Mr. Harmer raises seems to me to be equally 

 applicable under any view ; if, for example, the coast beds at Trim- 

 mingham are much above the level of Norwich why are they not, on Mr. 

 Harmer's view, intercalated between the crag at Thorpe and the beds 

 Mr. Harmer has identified with Mr. Wood's '•' middle drift." Surely 

 some cases ought to occur among the numerous exposures of Norwich 

 Crag in Norfolk, in which the Boulder-clay of the Cromer cliffs can be 

 seen to intervene between the Norwich Crag and Mr. Wood's " upper- 

 and-middle-drifts." The absence of Boalder-clay as the highest 

 member of the cliffs of the Norfolk coast (the equivalent of that in 

 High Suffolk) I have already admitted in my first paper might, on 

 Mr. Wood's views, be the result of denudation ; but its absence 

 throughout the district, wherever Boulder-clay is known to form the 

 base of the cliffs, is rather remarkable. Mr. Gunn and Mr. Wood I 

 am aware believe tliat it does exist in the low cliffs at Pakefield 

 and Corton, but if all tliree divisions of the drifts are developed at 

 these points, within a height of thirty or forty feet, it involves the 

 difiiculty of a great attenuation of Mr. Wood's two upper divisions 

 after they leave the high land and descend more than 200 feet to the 

 sea-level. At Corton, the assumed equivalent of Mr. Wood's " upper 

 Boulder-clay" is but from three to nine feet thick; at Hasboro' 

 ten feet ; whilst in High Suffolk the Boulder-clay attains a thickness 

 of at least sixty feet. 



The occurrence of derivative fossils would seem to be rather an 

 uncertain guide in the classification of the drift series. Mr. Taylor 

 (at page 238) observes that the coast clay has been formed princi- 

 pally by the wreck and denudation of the Lias (and the editor adds, 

 of the Kimmeridge clay) ; but this is really no distinctive feature, as 

 the Bedfordshire Boulder-clay, which is evidently an extension of 

 the High Suffolk clay, is literally loaded with these fossils, and the late 

 Mr. Trimmer (in the quotation given by Mr. Gunn) described his 

 "upper Boulder-clay" (the ''upper drift" of Mr. Wood) " as character- 

 ized by an abundance of oolitic detritus." Unless it is assumed that 

 the materials of the Boulder-clays have been derived from a distance, 

 and in each from different directions, it seems probable that succes- 

 sive deposits in the same localities should contain similar derivative 

 fossils. 



In the observations I have made I have wished rather to leave 

 the succession of the drift deposits an open question than to lay 

 down unequivocally any order of sequence. It is a subject that may 

 well be held in suspense, and the evidence in relation to it seems 

 scarcely of a nature to base exact conclusions upon, or to afford 

 materials for mapping out the various subordinate divisions of 



