•374 MR. ir. B. MILNER ON THE [vol. IxxVlii, 



In conclusion, it is hoped that the methods employed and the 

 results obtained from this investigation will indicate a possible 

 solution in other cases where palseontological evidence is scanty or 

 wanting; used cautiously and oyer limited areas, such petrographic 

 methods shonld prove invaluable to the stratigrapher. 



It remains for me to record my thanks to Prof. W. W. Watts, 

 By. H. H. Thomas, and Prof. P. G. H. Bos^vell for their kind help 

 durino- the course of this work. Mr. Gr. M. Part verA^ kindly 

 reproduced the kyanite-grains shown in figs. 2-4, and I am also 

 indebted to Mr. Gr. S. Sweeting for the assistance which he has 

 Tendered during the preparation of the manuscript. 



DlSCTJSSIOK^. 



Prof. P. Gr. H. Bosw^ELL welcomed the paper as a contribution 

 to our knowledge of the petrology of the Tertiary deposits of the 

 West of England. The Author's records of the characteristic 

 minerals were continued b}'' the speaker's own identifications. It 

 "was a noteworthy but unexplained fact that, while the Permian, 

 Trias, Lias, and Inferior Oolite of the West of England were 

 characterized by an abundance of garnet, that mineral was absent 

 from, or extremel}" rare in, the Cretaceous, Eocene, Oligocene, 

 and Pliocene of Devon and Cornwall, although it was a common 

 ■constituent of the Palaeozoic rocks of Devon, Cornwall, and 

 Britanny. 



He encjuired wh}^ the Author desired to have the staurolite in 

 the St. Keverne sands derived from the old ' Armorican ' land on 

 the south-west, unaccompanied by its usual associate, kyanite ; 

 ^vhile, in the case of the sands at St. Agnes and St. Erth, he 

 a-ssumed a Lower Greensand origin in the north-east for the same 

 two minerals. The absence of kyanite at St. Keverne seemed to be 

 inconclusive in the matter of the derivation of the material. 



The paper was valuable for the additional light which it threw 

 "upon early Pliocene geography. The Author's conclusions, although 

 novel, were not necessarily inconsistent with our ideas of the 

 distribution of Pliocene land obtained from a study of the fauna 

 'of the St. Erth claj's and the Crags. That the migration of 

 southern species into the North-Sea basin over what is now the 

 English Channel and Kent was possible in early Pliocene times, 

 I)ut was prevented during the deposition of the Middle and Upper 

 Pliocene, presumably by the raising of a land or shallow^- water 

 harrier, is indicated by the molluscan faunas. Further, the totally 

 different character of the mineral assemblages of the Cornish and 

 East Anglian Pliocene (the latter having apparently been derived 

 from the south-east) supports the view. Moreover, the similarity 

 in certain mineralogical respects (notably in the rarity of garnets) 

 ■of the Lenham Beds and the Cornish Pliocene may prove to be 

 more than mere coincidence* 



