the Chalk in the Counties near London. 357 



Loam-pit hill near Lewisham. 



Mouth of the Cavern on the side of Blackheath hill. 



Pit in Old Charlton on the south side of the Woolwich road. 



Great pit at New Charlton. 



Cliff' opposite Woolwich dock-yard. 



Pit at Erith. 



Three pits near the bank of the river Cray near Crayford. 



Pit on the north side of the churchyard at Dartford. 



Trenches dug for forming a common sewer near Gravesend, 

 on property belonging to Mr. Rosier. 



The entrance to the tunnel of the Thames and Medway 

 canal at Higham. 



On the north side of the Thames the localities observed 

 are, Purfleet, a pit on the west side and another on the east 

 side ofBelmont Castle near Grays, and a pit on the east side 

 of Grays; also a pit at George's Farm near Hertford. 



A similar stratum is seen at Newhaven in Sussex, and the 

 same flints have been seen in other counties, but not in their 

 original site. 



At Purfleet the name given to these flints is iron flints. The 



bed in which they are found is generally about eight or nine 



inches deep, seldom above a foot, and consists of a reddish 



clay with an abundance of oxide of iron. Scarcely any sand 



can be got from this clay by washing. It is stuck quite full 



of flints. Some of these flints are very small, not exceeding 



an inch in length; but the greater portion are three or four 



inches long, and some much longer. They are round, and 



terminating in a point at each end, and on the whole in form 



not unlike a cucumber. Some however are of a triangular 



form. The exterior is covered with a rough black crust, which 



is found to be a combination of silex and oxide of iron. 



When broken by the hammer the oxide of iron is found to 



penetrate about a quarter of an inch all round, and there are 



frequently streaks of iron further in the interior. The body 



of the flint is black, but decidedly distinct from the dark blue 



flints found in chalk. The fracture is conchoidal, but these 



flints, thoujjh not unmanageable, do not yield flakes in any 



direction so readily as the chalk flints. When burnt in the fire 



the exterior crust becomes reddish, and the rest of the flint is 



of a dirty while colour, not nearly so bright and beautiful as 



the porcelain substance made by burning chalk flints. It is 



exceedingly difficult, with ever so great caution, to get them 



burnt without cracking and flying in pieces. Such of these 



flints as have been exposed to the atmosphere have become 



j)arlially decomposed immediately under the black crust. 



I have been informed by two gun-flint makers that such 



