The Chalk. 227, 



about 1,200 feet thick in Dorsetshire, Hampshire, &c. 

 The Lower Chalk usually contains no flints and, as already 

 stated, is somewhat marly at the base, while the Upper 

 Chalk is interstratified with many beds of interrupted 

 flints. These are of irregular form, and lie in layers in 

 the lines of bedding. A great proportion of them are 

 stated by Dr. Bowerbank to be silicified Sponges, which 

 often inclose other organic bodies, such as shells, fragr 

 ments of Belemnites, &c.; others of large size, called 

 Paramoudras, which are rare, stand vertically across the 

 beds. These sometimes resemble, in general form r the 

 large cup-shaped sponges of the Indian Ocean Alcyonium, 

 or Neptune's cup. 



As a whole, the Chalk dips gently from its western 

 escarpment to the east and south, and round the Wealden 

 area to the south and north, underlying the Tertiary strata 

 of the Hampshire and London basins, and reappearing 

 with precisely the same characters on the coast of 

 France. Its area in Europe and Asia is immense. In 

 the north of Ireland, between Belfast and the Giant's 

 Causeway, there are patches of very hard Chalk on the 

 coast, overlaid by columnar basalt of Miocene age. 

 The great superincumbent pressure of these masses of 

 igneous rocks has hardened the chalk, and therefore 

 they have not, as is usually supposed, been altered by 

 the heat of overflowing lavas, except possibly for an 

 inch or two at the immediate point of junction, but 

 this is somewhat foreign to our present subject. 

 Traces of Chalk and Upper Greensand occur at Bogin- 

 garry, &c., in Aberdeenshire. These consist partly of 

 chalk flints, partly of sandstone, possibly in place, and 

 sufficient to show that Cretaceous rocks, which have 

 been removed by denudation, probably once spread over 

 that country. Cretaceous strata, discovered by Mr. 



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