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'UNIVERSITY 



SECONDARY AND TERTIARY SANDSff,^ 



little felspar. This rock near Whitby also contains 

 garnets, but the quartz has no fluid cavities ; the grains are -Ath of 

 an inch in diameter, and have their angles removed, but are sur- 

 rounded with crystalline quartz which forms the cement. The quartz 

 in this rock is such as might be obtained from the decomposition of 

 clay slates. Sand from the Portland Stone in Wiltshire is rounded, 

 quartzose, and contains few fluid cavities, generally without bubbles ; 

 the grains vary from -^th to ^J 5 th of an inch. They are associated 

 with but not enclosed by ovoid grains of carbonate of lime. 



In the Wealden Sands the quartz consists of slightly rounded 

 colourless grains almost free from fluid cavities, but enclosing some 

 hair-like crystals of rutile. The cement is partly carbonate, of lime, 

 partly flint. 



The Neocomian Sand called Carstone at Hunstanton is mainly 

 composed of rounded grains of quartz containing tourmaline and 

 rutile, with a few fluid cavities generally free from bubbles. This 

 quartz is mixed with small granules of dark-brown pisolite, and 

 contains a few scales of mica and a little felspar. The rock contains 

 less than 50 per cent, of silica and 30 per cent, of oxide of iron, 

 though sometimes the amount of iron is more, and the silica some- 

 what less. The Sevenoaks stone of the Lower Greensand consists 

 of chert, in which there are only occasional grains of quartz, some of 

 which are rounded, while others are angular. 



In the Hertfordshire Puddingstone, which occurs below the 

 London clay, the flint pebbles are united by a concrete, partly 

 formed of flint and partly of fragments of quartz. The quartz is all 

 angular, greatly in excess of the flint, and sometimes contains fluid 

 cavities. 



The brilliantly coloured sands of Alum Bay, of Lower Bagshot 

 age, like the Triassic and Permian sands, lose their colour when 

 boiled in hydrochloric acid. The quartz grains are all worn, though 

 not completely rounded ; occasionally they contain crystals of tour- 

 maline, and sometimes fluid cavities, but rarely enclose bubbles. 



In the Headon sands of Hordwell Cliff, all the quartz is com- 

 pletely rounded, and fluid cavities with bubbles are abundant. The 

 ruck contains no fragments of felspar. 



The marine beds at the top of the Hempstead series in the Isle 

 of Wight include sand composed of quartz grains which are well 

 rounded. 



The Boulder Clay at Holy well in Flintshire yields sand of a 

 varied character, some grains being small quartz pebbles, others 

 rounded particles of felspathic and other rocks. Some unworn 

 quartz grains derived from crystalline sandstones are observed, 

 associated with rounded grains derived from the millet-seed sand- 

 stone. 



This detailed analysis of some of the important beds of sand 



which occur in the British strata may serve to point out not only 



the great field which is open to further investigation by examination 



of the conditions under which the beds were accumulated, but is also 



VOL. i. G 



