174 NEOZOIC TIME. [CHAP. X. 



distant sources. These include blocks of granite, hyperite, 

 basalt, porphyrite, and felsite, with fragments of hard 

 Palaeozoic rocks and of quartzite schists and gneiss. Some 

 of them resemble Scotch and Norwegian rocks, but are 

 just as likely to have come from the north of Ireland. 

 From their number and general angularity it is believed 

 that these fragments were transported by floating ice 

 in the same way as similar blocks are now carried south- 

 ward by floating icebergs, and dropped on to the bottom 

 of the Atlantic at the present day. Their presence may at 

 any rate be regarded as indicating the influx of cold cur- 

 rents from more northern shores. 



The Chalk Marl is an impure chalk, containing in the 

 southern counties from 16 to 24 per cent, of fine sand and 

 silt, with small particles of glauconite. It was formed in 

 deeper water than the G-ault, and attains its greatest thick- 

 ness in and east of Berkshire, thinning both to the north 

 and to the south-west ; but as in the case of the Grault, the 

 thinning to the south-west is accompanied by an increase 

 in the proportion and size of the quartz grains, while 

 toward the north-east there is a diminution in the number 

 of recognizable quartz particles and of other inorganic 

 materials, with an increase of minute shell-fragments, and 

 of other calcareous materials. 1 



The outcrop of the Chalk Marl along the base of the 

 main escarpment from Dorset to Norfolk presents us with 

 a transverse section of a large lenticular mass of slowly 

 accumulated material, having its maximum thickness over 

 a tract which lay at some distance from the land, and yet 

 was not beyond the reach of currents bearing a certain 

 amount of finely-divided inorganic detritus, and from this 

 region of maximum development we can trace it into the 

 purely calcareous deposit of a deeper sea on the one hand, 



1 See W. Hill in " Quart. Journ. Geol. Soc.," vol. xliii. p. 582. 



