208 PROP. BOSWELL Otf THE CRETACEOUS AttD [voL Ixxix, 



been examined petrologically. The most complete section, which 

 is perhaps typical, despite the fact that the beds are rather 

 variable, is that exposed in the Goyle, south-west of Woodlands 

 and north of the Racecourse, on the Great Haldon Hills. 1 



On the Little Haldon Hills the best section at present visible is 

 that in Smallacombe Goyle on the eastern flank. The base of the 

 deposit is not reached, but a greater thickness of beds is seen than 

 on the Great Haldon. The section recorded by Mr. H. J. Lowe in 

 1899 is reproduced briefly below ; but, at the present time, only the 

 upper portion of Bed 5 and the succeeding beds are visible : — 



Thickness in 

 feet. 



1. Surface-soil and flint-gravel 7 to 9 



2. Sharp coarse yellow sand, containing- large irregular 



masses of chert 30 



3. Brownish sand without chert 15 



4. Rather coarse brownish greensand, with large grains of 



glauconite, including some lenticular seams of white sand. 7 



5. Denser and greener sand with lumps of cherty stone, 



current-bedded and showing some layers of darker green, 

 owing to the preponderance of glauconite-grains ; passing 

 down into glauconite- sand containing flattish lumps of 

 glauconite- sandstone 40 



Certain of the sandy beds, notabty those containing glauconite, 

 are moderately graded, but the majority of the deposits show little 

 evidence of sorting. 



Mechanical analyses of numerous samples were made, using 

 single-vessel elutriators (a separate vessel for each grade). Some 

 typical results, chosen to show the variation in composition, are 

 represented graphically in fig. 1 (p. 209). 



The minerals recognized in the Cretaceous deposits are 

 enumerated in the table on p. 226. 



The residue of density greater than 2 - 8 is abundant in all samples, 

 and is either black and lustrous as a result of the great quantity of 

 schorl present, or deep green from the abundance of glauconite. 



In the following notes, the mineral order adopted is approxi- 

 mately that of relative abundance. 



Tourmaline (schorl) usually constitutes the bulk of the 

 residue. The grains are of all sizes up to - 3 mm. in diameter, but 

 are generally many times larger than the other heavy detrital 

 minerals. The mineral occurs in irregular fragments, stumpy 

 prisms, networks of needles, or spherically radiating fibres. It 

 displays a wonderful range of colour, among the varieties seen being 

 grey, yellow, brown, pink, blue, green, and purple. Most of the 

 grains show the strong absorption characteristic of tourmaline. A 

 few approximately basal flakes occur, and among these nearly 

 triangular, zoned crystals have been noted. 



In many samples, muscovite is, after tourmaline, the most 

 abundant heavy mineral ; in others glauconite. The muscovite is 



1 Newton Abbot Memoir, p. 94. 



