16 



Martial pyrites, or sulfure of iron, is not uncommon in it, 

 either in full metallic splendor, or in different states of decom- 

 position passing into ochre or oxid of iron. It is remarkable 

 that Mr. Kirwan, in his Geological Essays, p. 338, says that 

 metallic substances are never found in chalk. Werner Kal. 

 Classif. 19. Berg. Kal. 233. Yet in France martial pyrites are 

 said to be found in it, 39 Roz.- 358 ; as if it were not found 

 in England. Pyrites are found in. the chalk of Sussex ; I have 

 found them from Dover to Margate ; at Godstone also in 

 great abundance, where the chalk in various ways passes into 

 fine-grained micaceous lime-stone called fire-stone, brought 

 in abundance from Ryegate. 



The upper figure is meant to represent a lump of chalk from 

 Sussex, which has a conical fracture not uncommon in chalk, 

 and sometimes in flint. The little granulse of fine gravel so 

 regularly formed about it, seem to be a filtration of water 

 carrying sand with it through some loose chalk, which meet- 

 ing with a more compact piece runs down the sides in drops, 

 and at the same time is absorbed by the chalk, leaving the 

 sand on the surface in little globules. There are sometimes 

 large quantities of sand in the chalk which fall in occasion- 

 ally, and are called by the workmen sand gulls. 



Middle figure. Chalk passing into lime-stone, hardening 

 with inosculating veins. 



The lower figure represents a piece of chalk rounded by 

 rolling about in the sea, perforated by the Mytilus rugosus, 

 or some species of Pholas : being stained it loses the appear- 

 ance of chalk. Harder substances are often perforated by 

 testaceous animals. 



Brj'tim calcareum, English Botany, t. 191, should seem 

 to indicate good chalk, as I have found the best where it 

 crows. 



