85 



cemented in other parts by means of a very little lime, and 

 more strongly still by a siliceous cement. The original of 

 the impression we do not at present know. The particles in 

 the left hand figure are somewhat larger, but are more 

 compactly agglutinated by the siliceous cement, and seem 

 as if more or less fused into each other, somewhat ap- 

 proaching the vitreous appearance. The impression seems 

 to belong to some vegetable, possibly furnished with spines 

 in the order where the little ovate knobs appear, which in a 

 specimen lent me by Sir Joseph Banks were rounder, his 

 whole specimen not being compressed*. The upper figure 

 with the long squamee is what is called by Kirwcm ferru- 

 ginous Sandstone, see v. 1. p. 365. It is coloured with an 

 oxide of iron, which seems to be in that state of oxygeniza- 

 tion on the outside, which has the conglutinating power 

 ascribed to it by Mr. Kirwan, and is consequently more 

 compact on the outside than on the inside. Pebble stones 

 held together in this manner are very common in gravelly 

 places about London. 



Tlie right hand upper figure is a coarser stone of a similar 

 nature, with some pebbles occasionally here and there about 

 it; also some lumps of a chalky appearance resembling de- 

 composing feltspar, if I may guess by the little remains of 

 the crystal and fracture. Thus it is perhaps next in order 



* I have figured the specimen given me by Mr. Martin of Derbyshire, as 

 it had an impression on it resembling a bamboo s*alk, although Sir Joseph 

 Banks's was better in other respects. 



