the Chalk in the Counties near Lo7idon. 359 



These flints are very large and of very irregular shape. 

 They bear some resemblance to very large blocks of flint 

 frequently seen towards the top of some chalk-pits. When 

 broken with the hammer, however, they present instead of* 

 the deep dark blue of the chalk flints a grayish surface, in 

 many parts whitish, as if composed of silex differently granu- 

 lated, and probably mixed with argillaceous or other matter. 

 When burnt in the fire they appear still more decidedly dif- 

 ferent in appearance. There are streaks of oxide of iron dif- 

 fused near the surface, and in many instances throughout the 

 whole mass. The whole flint has not been formed at once, 

 but one part has aggregated after another, and the divisions 

 are very perceptible to the eye. 



In the face of a fractured flint of this species is frequently 

 seen one dark black piece surrounded with a mass of grayish 

 flint, and sometimes more than one such dark piece. But 

 sometimes also there is a grayishpiece of flint surrounded by 

 black flint : many divisions in curved and generally circular 

 lines are perceptible. 



When burnt in the fire these flints separate into pieces, 

 leaving almost smooth surfaces on both sides at the places 

 of separation. These flints are totally useless for gun-flints 

 or for the porcelain manufacture, but are excellent for build- 

 ing. 



Such flints are well known at Northfleet, being found very 

 abundantly in the loam immediately over the chalk-pits near 

 to Gravesend. But the watery action there has been so con- 

 siderable that there is merely a thin stratum of diluvial matter 

 and vegetable mould over the chalk ; so that although I have 

 known of them for several years past, it was not until a few 

 months past I discovered them in situ in the places already 

 stated. They are not unfrequently seen in the fields in the 

 counties round London where the chalk comes up near to the 

 surface. If a name be given to them it might be the gJ'ay 

 iron flint. 



In this flint I have found at Northfleet abundance of Echini, 

 the Echinocorys, Scutatus, Conulus, and Spatangiis, generally 

 much crushed, and the shells ^themselves totally gone, pro- 

 bably corroded and destroyed by the oxide of iron. 



Mr. Parkinson, in a paper published in the first volume of 

 the Geological Transactions, has remarked the difference of 

 the casts found in the gravel from the casts found in the chalk, 

 and contends that they are of different origin. I have no 

 doubt they are the same species as those in the chalk, and 

 that this bed which I have attempted to describe is the original 

 habitat of the fossils to which he refers. 



