SOIL OF THE UrPER AND LOWER CHALKS. 243 



II. The Secondary Strata — contain no animal remains which 

 can be identified with existing species. Those which are found in them 

 are nearly all different from those which occur either in the tertiary 

 above or the primary strata below. 



A. — Cretaceous System. 

 5°. Chalk. 600 ft. The upper part softer, and contain- 



ing layers of flints, witli many marine 

 ^ remains. Below, the chalk is harder, 



and towards the bottom passes into 

 beds of marl — (chalk marl). 



Extent. — The chalk occupies a very large area in the south-eastern part of 

 the island. It forms a broad band of from 15 to 25 miles in breadth, running 

 north-east and south-west from the extreme south-western part of Dorset, to 

 the extreme north of Norfolk, — it there turns nearly at a right angle, into the 

 centre of Lincolnshire, where it is 10 to 15 miles in breadth, and thence stretches 

 into Yorkshire, in the south-eastern part of which county it covers a large area, 

 and about Flamborough Head attains a breadth of 35 miles. In passing 

 through Berkshire and Suirey, it is partially interrupted by the plastic clay 

 which it embraces on every side ; and hence, in following the outline of this for- 

 mation it encircles with a broad fringe the southern edges of Sussex and Surrey 

 and the northern borders of Kent. 



Soil. — The soils formed from the upper chalk are all more or less mixed 

 with flints, and they produce naturally a very short but excellent sheep pasture. 

 A great portion of this chalk-land in Dorset, Wilts, and Berks, has been occu- 

 pied as a sheep-walk for ages, though under proper cultivation it is said to be 

 convertible into good arable land, producing oarley, turnips, wheat, and sain- 

 foin. The lower chalk soils (chalk marl) consist of a deep, strong, calcareous 

 grey or white loam, very productive, and when mixed with the green sand be- 

 low it, becoming still richer, more friable, and more productive of every kind of 

 crop. It is better suited for wheat than tlie upper chalk, but is less adapted for 

 turnips. 



The porous nature of the chalk renders the soil very dry, and in many locali- 

 ties th^e only method of obtaining a sufiicient supply of water is by forming 

 ponds to catch and retain the rain-water. 



In Norfolk and Suffolk, on the Lincolnshire, and more recently on the York- 

 shire Wolds, great improvement has been effected by dressing the chalk-soil 

 with fresh chalk brought up from a considerable depth below, and laid on at the 

 rate of 50 to 80 cubic yards per acre. The explanation of this procedure is to 

 be found in the fact above stated, that the lower chalk marls, without flints, pro- 

 duce an excellent soil, fitted therefore, by admixture with the poorer upper-chalk 

 soils, for materially improving their quality. It is, therefore, only in localities 

 v/here this lower chalk can be obtained, that the above method of improve- 

 ment can be with any material advantage adopted. This is proved by the 

 practice at Sudbury, in Suff"olk, which rests upon the upper beds, where it is 

 found to be more profitable to import the lower chalk from Kent, to lay upon 

 these lands, than to dress them with any of the chalks (only upper beds) which 

 are immediately within their reach.* 



6°. Green Sand. 500 ft. The upper beds consist of layers of 



a Upper, 100. a greenish sand or sand-stone, often 



b GaiUt, 150, chalky. The gault is a solid compact 



c Lower, 250. mass of an impervious blue clay, some- 



times marly. The lower green sand 

 contains a series of ochrey resting on a 



• A. rigorous chemical analysis of characteristic specimens of these two chalks might lead 

 to interesting results. 



