Outlines of Geology* 31 



stone, it constitutes a soil not unpropitious to the growth of 

 several forest trees, and even bears very stately oaks. Near 

 Woburn, in Bedfordshire, this sand is largely planted with firs ; 

 and there, as well as at Ryegate, in Surrey, it contains large beds 

 of fuller's earth. The organic remains which it contains in 

 greatest abundance are nautili and cornua ammonis. This for- 

 mation may be traced with little interruption from the neighbour- 

 hood of Shaftesbury in Dorsetshire, to St. Neots, in Huntingdon* 

 shire. It appears again on the east coast of Norfolk ; reappears 

 at Spilsby in Lincolnshire, and again in Yorkshire, where it 

 reaches the north coast of that county, and covers much of its 

 western district. In many places this sand is associated with 

 and overlies several varieties of clay of different texture and 

 and composition, and often assuming a slaty aspect, and contain- 

 ing bituminous substances, pyrites, and in some places, as about 

 Whitby in Yorkshire, a considerable quantity of sulphate of 

 alumina. On the south coast of England, as, for instance, in the 

 Isle of Purbeck, this shale is abundantly bituminous, and forms 

 what is called Kimmeridge coal. Organic remains are not rare 

 in it ; and in Wiltshire, it is associated with several varieties of 

 limestone, in which they are extremely abundant. It is, however, 

 doubtful, whether these substances should not rather be referred 

 to the oolite formation, which is extremely extensive, and which 

 is seen in the map proceeding from Somersetshire to the banks 

 of the Humber in Lincolnshire. Carbonate of lime is its leading 

 ingredient, and several of its varieties are used as building mate- 

 rials, such as Bath, Purbeck, and Portland Stone. Its texture, 

 however, is such, that it is generally easily acted upon by the 

 weather, and it is difficult to suggest any good criterion by which 

 its relative durability may be judged of. It is sometimes sup- 

 posed, that a comparative estimate of its value and permanency 

 may be founded upon its absorbent powers, in regard to water, 

 but this is not always strictly true ; that which abounds in shells 

 and other organic remains is generally very subject to decay. 



In the quarries in the isle of Portland, three distinct strata are 

 visible j the uppermost called by the quarrymen the cap, consists 



