256 THE WORLDS LUMBER ROOM. 



largely composed. The silicious flags of Caithness, for 

 instance, are impregnated with oily matter which is 

 apparently due to the innumerable fishes embedded in 

 them. 



Shells and the like are some of the most indestructible 

 of animal remains ; but having already spoken of the vast 

 accumulations of chalk and lime to which they have given 

 rise, we need only add that the soft earthy carbonate of 

 lime called "marl," which is formed of freshwater shells and 

 occurs in layers and patches from one to several feet thick 

 in bogs and old lake sites, was at one time dug or dredged 

 up as manure for the pastures. 



The importance of lime and especially phosphate of 

 lime to many crops may be seen by a glance at the mineral 

 composition of their ash. 



Thus the ash of meadow hay contains 1 1 *6 per cent, of 

 lime and 6-2 of phosphorus ; that of winter wheat 4*9 of 

 lime and 7-4 of phosphorus ; and that of red clover has 34*0 

 per cent, of lime and 9 '9 of phosphorus. 



" Shell sand " (consisting of shelly, coralline, and other 

 limy debris) is often applied to clay soils, especially tjy the 

 French, who value it highly; and though 100,000 tons are 

 taken every year from Padstow Harbour, it is so abundant 

 that much more might be used. 



The name of "fossil" is given to all organic bodies, 

 animal or vegetable, which have been naturally buried and 

 more or less petrified or turned to stone. 



Many fossil shells are, however, scarcely at all altered, and 

 some even of the more ancient still retain not only their 

 mother-of-pearl, but even their colouring. In others again, 



