part 2] TERTIARY OUTLIERS OF THE WEST OF ENGLAND. 217 



pure Eocene. So far as the petrology is concerned, however, the 

 Eocene deposits of localities so far apart as Mount's Bay and the 

 Haldon Hills might conceivably be very different. 



It is satisfactory, nevertheless, to note that the petrology of 

 the North Devon outlier resembles that of the Eocene material 

 from the Haldon Hills. Corundum is more plentiful in the latter, 

 and monazite in the former ; but no important difference in the 

 mineral assemblages was observed. 



(3) The Oligocene (Aquitanian) Deposits. 



When we turn to the two basins of lignitic clays and sands, the 

 one near Torrington, and the other between Bovey Tracey and 

 Newton Abbot, we observe notable differences in lithology and 

 petrology from the deposits previously described. 



Bovey Beds. — The Bovey deposits are well known, and have 

 an extensive literature. They rest upon Devonian, Culm, and 

 Permian rocks. In altitude they never rise to more than 

 500 feet above Ordnance-datum, and they have not been bot- 

 tomed, although a depth of 500 feet has been proved. Clement 

 Reid considered, too, that at least another 400 feet had been 

 removed by denudation. The basin would thus originally have 

 been over 1000 feet deep. The beds occupy at present a lozenge- 

 shaped area, about 9 miles long and 4 miles broad, and they vary 

 considerably in lithology, from fine-grained fire-clays to coarse 

 gravels. In some of the gravelly and sandy streaks, schorl 

 constitutes as much as 25 per cent. The results of the mechanical 

 analyses (see fig. 5, p. 219) serve to emphasize this variation, and 

 indicate, moreover, the incomplete character of the grading of the 

 deposits, the bulk of which are unsorted clayey sands. Marine 

 action or even prolonged river-action would have resulted in a 

 certain amount of sorting, and a separation into sands and 

 kaolin-bearing clays. The materials as they are found, however, 

 indicate deposition of various grades, coarse and fine, resulting 

 from the sudden arrest of streams of detritus-laden water as it 

 entered a lake-basin practically free from currents. Only the 

 proximity of an area of kaolinized and tourmalinized granite 

 could have given rise to such sediments. 



The heavy detrital minerals identified are enumerated on p. 226. 



The quantity of heavy minerals in the different samples varies 

 considerably, being at times far below - 01 per cent. Where the- 

 proportion of the residue is considerable, schorl constitutes the 

 bulk. Other minerals rarely occur in quantity. The relative- 

 proportion of the various species present does not appear to vary 

 from Bovey to Newton Abbot. 



The assemblage is actually far less rich and more restricted 

 than the list of minerals might suggest. The only commonly- 

 occurring minei'als are the iron-ores, zircon, rutile, and tourmaline, 

 an assemblage without definite character. 



