part 2] CRETACEOUS AND TERTIARY OUTLIERS. 215 



Monazite occurs rarely in grains of the usual form. The 

 identification of this mineral was confirmed spectroscopically. 



' Garnet is also rare, a single grain, O08 mm. in diameter, 

 having alone been found. 



Quartz occurs, either as large rounded grains (1 mm. or more 

 in diameter), or in small angular chips (015 mm. in diameter). 



All the minerals enumerated above (with the exception of the 

 rare staurolite and kyanite, which may have been obtained from 

 the Greensand) could have arisen from the erosion of the Dart- 

 moor or Bodmin granite-masses. 



The Haldon Hills. — Capping the flat-topped hills of Great 

 and Little Haldon are beds of coarse gravel with a grey, yellow, or 

 brown matrix, and occasional seams of sand and mealy clay. As 

 Clement Reid (who described these deposits and suggested for 

 them an Eocene age) 1 pointed out, they reach the top of the 

 Haldons, approximately 800 feet above Ordnance-datum, but are 

 subject to sagging round the edge. There is no evidence, however, 

 that they descend into neighbouring valleys, and they are probably 

 not more than 30 or 40 feet thick. The bulk of the gravel 

 consists of large well-weathered Chalk-flints ; but Greensand chert 

 and fragments of Palaeozoic rocks also occur. The wide extent of 

 the gravels and the immense amount of flint contained in them 

 gives some indication of the huge quantity of chalk which has 

 disappeared. 



Derived Upper Chalk fossils such as Echinoco?^ys are found. 

 The deposits are thus Tertiary in age, and, on account of their 

 position and general similarity to certain gravels of Bagshot age, 

 they have been referred to the Eocene. 



Clay is more prevalent than sand in the matrix of the gravels, 

 and is clearly derived from the decomposition of felspar yielded by 

 the granite farther west. The matrix is greyish to yellow or 

 brown when ironstained. The sands are often clayey, and are 

 badly graded, as the accompanying graphical representation of the 

 results of mechanical analyses indicates (fig. 2, p. 214). 



The mineral assemblage is an interesting one, as indicated in the 

 table on p. 226. 



The heavy residue is usually large in quantity, and presents 

 a lustrous black appearance due to the large proportion of schorl 

 present. Small local differences in the relative proportions of the 

 minerals present have been noted, but all the deposits are of the 

 same general type. The detrital minerals are poorly graded, topaz 

 and tourmaline being very large (see fig. 3, p. 214). 



Tourmaline is exceedingly abundant, and is found in grains 

 of all colours, shapes, and sizes. Small prismatic crystals are 

 abundant, many being fluted. 



Topaz is, on the whole, very plentiful. It occurs in large, 



1 Newton Abbot Memoir, p. 102. 



q2 



