S64 Proceedings of 1 
acean: with the strata, therefore, of this 
ibriaation, these remarks commer.ee. 
BessofSakd and Gravel. 
The sands of tiiis formation vary in 
colour from white, which is most rare, 
tiirough different sliades of yellow up to 
orange-red; the colour proceeding partly 
from a ferruginous stain on the surface of 
die particles of sand, and partly from the 
intermixture of yellow oxide of iron. 
Particles of those sands, which are dis¬ 
posed in distinct seams or beds, w’hen 
examined by the microscope, 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 re¬ 
spect, an uniform crystalline deposition. 
Tiiose sands, on the contrary, which, 
blended with broken and unbroken peb¬ 
bles, form gravel, appear, when thus ex¬ 
amined, to be mostly opake, to be va¬ 
riously coloured, and to be marker! with 
■conclioidal depressions and eminences, 
die result of fracture. 
The pebbles of this formation appear 
to be of four kinds ; 1st. Various pieces 
of jasper, gritstone, wlnte semi-trans¬ 
parent quartz, and other rocks. These 
have acquired, in general, smooth sur¬ 
faces and roundish forms, evidently from 
attrition, and exhibit no traces of orga¬ 
nization, excep't when, as is very rarely 
the case, the substance of the pebble is 
jasperized wood. The white quartz peb¬ 
bles, like quartz crystals, on being rubbed 
together, emit a strong white lambent 
light, with a red fiery streak on the line 
of collision, and an odour which much 
resembles that of the electric aura. 
2d, Oval, or roundish, and rather fiat 
silicious 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 substance is composed. In some 
this is spotted, or clouded, in very beau¬ 
tiful forms; in others it is marked by 
concentric stritE, as if the result of the 
successive application of distinct lamina ; 
the prevailing colours in most of these 
pebbles being different shades of yellow. 
In several, the traces of marine re¬ 
mains are observable: these are, in some 
the casts of aiiomm^ and the impressions 
of the spines and plates of echini, and in 
others, which generally possess a degree 
of transparency, the remains of alcyonia. 
The impiessions, though frequently on 
the surface of the pebble, seldom, if 
learned SocietiCo, 
ever, appear to be in the least rubbed 
down ; thus seeming to prove decidedly, 
that these pebbles have not been rounded 
by rolling, but that they owe their figures 
to the circumstances under which they 
were originally formed: it ts appre¬ 
hended, therefore, that these pebbles 
have each been produced by a distinct 
chemical formation, which, it may be 
safely concluded from the remains of 
marine animals so frequently found in 
them, took place at the bottom of the 
sea, while these animals W'ere yet living. 
The formation of these fossils at thfe 
bottom of a former sea, and perhaps on 
tfie identical spots in which they are 
now frequently, found, is more plainly 
evinced by pebbles agreeing in some 
peculiar characters being found to¬ 
gether in particular spots. Thus those 
in the county of Essex, ten miles north¬ 
ward of London, contain a much greater 
proportion of argil and iron than those 
met with in many other places; hence 
their colnur.s are darker, and the deli¬ 
neations which tlieir sections display, 
are very strong and decided, sometimes 
rhjsely agreeing with those seen in the 
Egyptian pebbles.* Passing on into 
Hertfordshire, pebbles of a very different 
character are found ; their crust is nearly 
black, and their section displays delicate 
tints of blue, red, and yellow, disposed 
on a dead-white ground in very beautiful 
forms. In another part of the same 
county occurs the pebble of the pudding- 
stone, which also presents peculiar cha¬ 
racters of colour, &c. 
Sd. Large tuberous, or rather ramose, 
irregularly-formed flints, somewhat re¬ 
sembling in figure the flints which are 
found in chalk, materially differing how¬ 
ever from them, not only in the colour 
of their external coat, which is of va¬ 
rious shades of brown, but also in that 
of their substance, which is seldom 
black, but exhibits shades of yellow or 
brown, in which red likewise is some¬ 
times perceptible. The traces of or¬ 
ganic structure, particularly of the alcy~ 
onium, occasionally seen in these stones, 
determine them also to have been formed 
at the bottom of the sea. 
* The gravel pebbles of Epping Forest are 
of this description; and cn most of the 
grounds leading down from the forest to the 
hamlet of Seward-stone, and to the town of 
Waltham, white, opake, and partly decom¬ 
posed, pebbles, are frequently seen, in which 
the argil and iron have been removed, and 
the silex only has remained. 
4;th, Pebbles^ 
