part 2] TERTIARY OUTLIERS OP THE WEST OE ENGLAND. 229 



Pliocene. 



(12) The Pliocene deposits, like the Cretaceous, are marine and 

 glauconitic. From their position and petrographic char- 

 acters they indicate a widespread submergence of the 

 Oligocene land-area. For the greater part, the detritus 

 is moderately well-sorted, and derived from a wider area 

 than any of the other Tertiary deposits. The assemblage 

 of heavy detrital minerals is abundant, varied, and poly- 

 genetic. 



For fruitful discussion of several of the matters dealt with in 

 this paper I desire to express my thanks to Mr. Henry Dewey. 

 For critically reading the manuscript, and for the preparation of 

 much material in the laboratory, I gratefully acknowledge the 

 assistance of Mr. J. G. A. Skerl. 



Discusston. 



Mr. H. B. Milner drew attention to the deposits at Orleigh 

 Court (near Bideford) which the Author had described as 

 Eocene (?). He (the speaker) had examined the mineral residues 

 from this deposit, and was impressed by then' strong resemblance 

 to the Pliocene beds of Cornwall. The Orleigh- Court material 

 presented the same andalusite, topaz, kyanite, and typical flat 

 tourmaline-grains, among others, as those met with in the Cornish 

 deposits; and, on account of this, and the fact that the situation 

 of the Orleigh-Court outlier was in accordance with the theory of 

 pre-Pliocene drainage previously advanced by him, he was more 

 inclined to regard the material as being of Pliocene age. 



With regard to the Author's remarks on ilmenite and magnetite, 

 the speaker agreed as to the general rarity of the latter in sedi- 

 ments, both in this country and in the alluvial deposits of Ceylon, 

 Brazil, and West Africa. A criterion of differentiation between 

 the two species was a crimson, combined with a dull metallic lustre 

 (seen with strong incident light) in the case of ilmenite, and the 

 adamantine silveiy-grey lustre reflected from highly-facetted grains 

 (like ' pin-points ') in the case of magnetite. 



He also drew attention to the Author's mode of recording the 

 results of petrographic examination of samples, and .urged the 

 general adoption of Prof. Watts's suggestion that numbers should 

 be used to replace letters ; comparison of numbers — by the mental 

 picture conveyed — was of far greater help in assessing the 

 frequency of species, especially where the correlation of many 

 samples had to be undertaken. 



Prof. W. W. Watts referred to the fragments in the Teign- 

 muuth Permian breccias, and enquired whether the evidence given 

 by them was in agreement with the Author's view as to the late 

 exposure of the Dartmoor granite-mass. He also wished to know 

 whether the Author agreed with Mr. Clement Reid's attribution 



Q. J. a. S. No. 314. r 



