part 4] PLIOCENE deposits or coRisrwALL. 375- 



Mr. Gr. M. Paet said that he had hoped that this paper might 

 suggest some reasonable source for the yevj similar assemblage of 

 minerals found in some of the (llacial drifts of Pembrokeshire, 

 which it could onlv be surmised were derived from some similar- 

 Tertiary deposit. As the Pembrokeshire drifts were derived from 

 a wester]}^ or north-westerlj direction, this would involve a northern 

 drainage, if Cornwall had provided any of the material for a deposit 

 from which the blood-red pleochroic andalusite had found its way- 

 into the gravels. 



Dr. H. H. Thomas ao-reed with the Author that the kyanite 

 of these deposits was most probabl}^ derived from sediments of' 

 Cretaceous age. The absence of kyanite from the Western New 

 Ked rocks was strong evidence in support of the Author's view. 

 He thought that the grains of staurolite with frayed-out cleavages, 

 owed this distinctive character to their derivation from large 

 crystals : that was the conclusion to which he had come from a 

 study of the abundant and large grains found in the Western' 

 Trias. With regard to the great similarity between the mineral 

 assemblages of the Cornish Pliocene and the drift-sands of Pem- 

 brokeshire, he had many years ago suggested the latter' s partial 

 derivation from Tertiary deposits occupying, in Glacial times, a. 

 position in the bed of the Irish Sea. 



Mr. Gr. Baeeow was greath^ interested in the Author's work, as- 

 it dealt with what are commonly known as Pliocene deposits, now 

 occurring at heights much above sea-level. The Geologists' 

 Association had taken a special interest in these high-level deposits,, 

 which occurred in patches extending from the south-east of Kent 

 at least as far as the neighbourhood of the Guildford gap in the- 

 Chalk. Apart from the Lenham Beds, fragments of undoubtedly- 

 marine shells have been found in the gravels of Headley Heath.. 

 The mode of occurrence of these is important, as it suggests where 

 to look for further casts. The}^ occur only when the sand sur- 

 rounding the original shell-fragments has been firmly cemented 

 by iron-oxide, and nowhere else. The examination of the deposit 

 on the ground suggests that these gravels are beach-deposits, with' 



broken shell-frao-ments once common in them. All these fraff- 

 . . . ^ 



ments have been dissolved ; but, where iron-oxide filtered in and 



cemented the sand before solution took place, casts of some frag- 

 ments are preserved. It is in such cemented patches that we must 

 in future look for evidence of the as^e and nature of these beds ; 

 this knowledge not only shows where to look, but where it is use- 

 less to look, and this so far covers more than 90 per cent, of the 

 whole. 



Mr. T. Ceook said that it was particularly pleasing to note the- 

 emphasis laid on sampling. Failure to record a mineral in such 

 deposits did not necessarily mean that the mineral was absent ; 

 but, with careful sampling, such as the Author appeared to have 

 carried out, much better results were likely to be obtained than^ 

 w^hen records were made on specimens eollected haphazard. It, 



