220 PBOF. BOSWELL ON THE CBETACEOTTS AND [vol. lxxix, 



cent.) and fine in grain (average diameter O05 mm.). Moreover, 

 the assemblage is very restricted, and consists of stable minerals. 

 Hornblende, epidote, and andalusite are records of single grains. 

 Topaz is also uncommon. 



Staurolite occurs in grains of diameter O06 mm. to 02 mm. 

 One grain was notably ragged. 



Grlauconite occurs in grains up to 05 mm. in diameter, and as- 

 foraminiferal casts. It is obviously derivative from some older 

 (probably Cretaceous) deposit. 



The extremely local character of the above assemblage of 

 minerals is again noteworthy. Grlauconite and, possibly, staurolite 

 seem to have been derived from other sediments, kyanite and 

 garnet are absent, and pleochroic andalusite is rare. The 

 minerals might almost have been obtained exclusively from the 

 Dartmoor granite, and the similarity to those of the Bovey Beds 

 needs no emphasis. Indeed, the assemblage is even poorer in, 

 species and of more restricted derivation. 



Fig. 6. — Chiastolite-grains. X 100 diameters.. 



[6 a is from the Oligocene Bovey Beds, Heathfield ; 6 b is from gravel 

 at Biddaford, of doubtful age.] 



The Cretaceous, Eocene, and Oligocene outliers thus yield 

 evidence from their petrography of the progressive restriction 

 of the area of rocks from which they were derived. The Cre- 

 taceous deposits are marine, often well-sorted, and contain far- 

 travelled minerals foreign to Devon and Cornwall, as well as local 

 varieties. The Eocene deposits are probably fluviatile, not well- 

 graded, and possibly contain some Cornish detritus, but few 

 ' foreign ' minerals. The Oligocene deposits are lake-like in 

 occurrence, badly graded, and of restricted and entirely local 

 derivation. 



