80 



amongst farmers as the blue marl. . From the soft condition of the 

 shelly matter which it contains, and the predominance of clay in its 

 composition, this has been found peculiarly serviceable when applied 

 to the more arenaceous varieties of soil. In the quantity of calcare- 

 ous matter which it contains, it is usually inferior to the beds of a 

 white or brown colour, which in many places rest above it, though 

 it is not to be inferred that in many instances it may not prove 

 equally advantageous to the land. The colouring matter of the clay 

 appears in part to consist of a carbonaceous matter, derived proba- 

 bly from the organic materials originally associated with the shells, 

 and often in part of a minutely divided greensand, either of which 

 ingredients might be expected to aid the calcareous and clayey mat- 

 ter in benefiting the soil. 



Of the hard Ferruginous Marl. — In some localities the beds con- 

 sist of shells more or less broken, intermixed with a brown ferrugi- 

 nous sandy clay, and often cemented with these materials into 

 masses which are broken with some difficulty. These, although 

 rich in calcareous matter, must obviously, from their mechanical tex- 

 ture, prove less valuable than either of the former. To this class, 

 also, may be referred the shell rock, and fragmentary masses ap- 

 proaching to limestone, which occur in various places. 



From the large per centage of carbonate of lime, which these con- 

 tain, there can be no doubt that, by burning, they might be con- 

 verted into a highly valuable lime. A specimen from the cliff at 

 York, yielded eighty-seven per cent, of calcareous carbonate, as 

 large a proportion as most of the valley limestone have been found 

 to contain : computing the quantity of caustic lime, corresponding to 

 this, we find that one hundred pounds of the shell rock would yield 

 48.7 pounds of strong lime. It is, therefore, well worthy of consider- 

 ation, whether the conversion of this material into lime, might not 

 be an object of profitable enterprise. In the neighbourhood of York 

 and other places, where it occurs, rock of sufficient hardness might 

 be obtained in great abundance and at comparatively little cost ; and 

 the cheapness of fuel would render the operation of burning, one of 

 moderate expense. That much of this rock, when exposed to 

 intense heat, would fall to pieces, and thus injure the value of the 

 product for distant use, is undoubtedly true. But there is also 

 much of it found in bands throughout the cliff, which has almost as 

 great solidity and permanency in the fire, as a secondary limestone, 

 and from this, a lime of superior character might unquestionably be 



