a?id on the Fossil Remains contained in them. ' 133 



are very abundant, are rarely seen in the counties adjacent 

 to the metropolis. This remark is rendered necessary, 

 since those widely extended beds of sand and gravel, with 

 sandy clav, sometimes intermixed and sometimes interposed, 

 and which have been generally hitherto considered as alluvial 

 beds, are here assumed to be the last or newest strata of 

 this island, slowly deposited by a pre-existent ocean : with 

 the strata, therefore, of this formation, these remarks com- 

 mence. 



Bkds of Sand and Gravfx. — The sands of this forma- 

 tion vary in colour from white, which is most rare, through 

 different shades of yellow up to orange red : the colour pro- 

 ceeding partly fron) a ferruginous stain on the surface of the 

 particles of sand, and partly from the intermixture of yellow 

 oxide of iron. Particles of those sands, which are disposed 

 in distinct seams or beds, when examined by the micro- 

 scope, are found to be transparent, most of them angular, 

 but some a little rounded, with all their surfaces smooth, 

 having no appearance of fracture, and resembling, in every 

 respect, an uniform crystalline deposition. Those sands on 

 the contrary, which blended with broken and uabrok«n 

 pebbles form gravel, appear, when thus examined, to be 

 mostly opake, to be variously coloured, and to be marked 

 with conchoidal depressions and eminences, the result of 

 fracture. 



The pebbles of this formation appear to be of four kinds; 

 1st. Various pieces of jasper, gritstone, white semi trans- 

 parent quartz, and other rocks. These have acquired, in 

 general, smooth surfaces and roundish forms, evidently from 

 attrition, and exhibit no traces of organization, except when, 

 as is very rarely the case, the substance of the pebble is 

 jaspenzed wood. The white quartz pebbles, like (luartz cry- 

 stals, on being rubbed together, emit a strono; white lambent 

 light, with a red fiery streak on the line of collision, and 

 an odour which mnch resembles that of the electric aura. 



2d. Oval or roundish, and rather flat siliceous pebbles, 

 generally surrounded by a crust or coat differing in colour 

 and degree of transparency from the internal substance, 

 which also varies in different specimens, in these respects, 

 as well as in the disposition of the parts of which the sub- 

 stance is composed. In some this is spotted, or clouded, 

 in very beautiful forms ; in others it is marked by concen- 

 tric striae, as if the result of the successive application of 

 distinct larpmoe : the prevailing colours in most of these 

 pebbles being different shades of yellow. In several ih^ 

 traces of marine remains are observable : these are, in some 



I 3 the 



