RELATIVES OF THE OYSTER. 2 I I 



utmost result, and thence would originate other mountain 

 masses which, to say the least, would be very nearly allied 

 to those which we term granitic." 



Surprising as it may be to many to find the shells of 

 oysters largely contributing to the crust of the globe, it is 

 still more so that creatures of extreme minuteness should 

 be associated with them. The Egyptian pyramids are 

 actually built of a limestone entirely composed of cham- 

 bered shells, exquisitely constructed, and of very small 

 size. Other rocks there are whose very substance consists 

 of microscopic shells of extraordinary beauty, once the 

 habitation of minute animals. No one who visits the 

 county of Kent, for instance, can fail to observe the exten- 

 sion of the great chalk range, which again shows itself on 

 the opposite coast of Boulogne. Above the chalk lies a 

 deep bed of plastic clay, and above this the London clay, 

 of which the hills of the Isle of Sheppey consist, and also 

 Shooter's Hill, which is about four hundred and forty feet 

 in height. Near Pegwell Bay, which is a pleasant walk 

 from Ramsgate, this London clay immediately covers the 

 chalk, spreading over a tract of no great extent. In some 

 parts, as, for example, a strip from the valley of the Darent 

 to below Gravesend, the overlying clays have been more or 

 less completely washed away, the chalk being with a mix- 

 ture of sand and vegetable soil, (o) " If all the points at 

 which true chalk occurs were circumscribed, they would 

 lie within an irregular oval about 3000 miles in long dia-' 

 meter the area of which would be as great as that of 

 Europe, and would many times exceed that of the largest 

 existing inland sea, the Mediterranean." 



(o) " Adventures of an Oyster," p. 73. 



