part 2] TERTIARY OUTLIERS OF THE WEST OF ENGLAND. 227 



the eastern deposits is doubtless on the south-east, namely, the 

 metamorphosed Palaeozoic rocks of the Southern Ardennes. It is 

 noteworthy that the Pliocene of Belgium resembles generally that 

 of East Anglia in its petrography. 



The case of the Lower Pliocene outliers on the North Downs at 

 Lenham, Netley Heath, Newlands Corner, etc., is, however, 

 different. 1 The mineral assemblage of these deposits is more 

 varied than that of the Cornish Pliocene ; but in one important 

 respect, namely, that of the great rarity of garnets, the two- 

 series of deposits resemble one another. 



V. Summary of Conclusions. 

 The main conclusions to be drawn are as follows : — 

 General . 



(1) The Cretaceous and Tertiary outliers of Devon and Corn- 



wall are linked broadly one with the other on petrological 

 grounds. 



(2) Their mineral assemblages differ radically from those of the 



Permian, Trias, or Lias-Inferior Oolite of the West of 

 England, in that they contain more material derived 

 from British and less from ' Armorican ' rocks. 



(3) On the whole, the deposits are moderately-well graded. Cer- 



tain of the Pliocene sands form exceptions to this rule. 

 Many of the Cretaceous deposits are poorly graded, and 

 many of the Eocene badly. Greater differentiation has. 

 taken place in the Oligocene and Pliocene deposits. 

 These lithological variations throw light on the mode of 

 origin of the various deposits, as indicated below. 



(4) Tourmaline, in grains of all sizes, shapes, and colours is by 



far the most abundant mineral throughout. It is. 

 obviously derived from the granite-masses and their 

 aureoles. 



(5) Andalusite and topaz may, in addition to tourmaline, be 



regarded as the characteristic minerals ; they are of local, 

 origin. 



(6) Garnet is rare or absent in all the deposits, despite its. 



abundance in the igneous and metamorphic rocks of 

 Devon, Cornwall, and Britanny, and in the Permian, 

 Triassic, and Lias-Inferior Oolite of Devon and Dorset. 



(7) Kyanite and staurolite occur plentifully in the Cretaceous, 



and Pliocene deposits, their source probably lying in the 

 old Armorican land-mass which was situated on the 

 south-west. 



(8) As the Upper Greensand and Upper Eocene deposits are- 



traced eastwards, topaz and andalusite occur in decreasing 

 quantity. 



1 See G. Macdonald Davies, op. cit. p. 82 ; also Proc. Geol. Assoc, vol. xxviii 

 (1917) p. 49. 



