and Mineralogical Observations . 
359 
1830 ,] 
selves, in and forming a part of the mass, which they were supposed to do, according 
, to that theory. This idea of their origin was certainly that generally received, as the 
most probable of the two, by the geologists of this country, hut still no very con- 
clusive fact was obtained ; some of the observations were contradictory, and 
many were questioned, as resting on doubtful authority, or as incorrectly made, from 
the difficulty which often attends the making geological observations ; and also, 
perhaps, from the supporters of each theory, in the mode they sawthings, reconcil- 
ing them, in some measure, to their previously formed ideas of formation. 
Attention has been lately directed chiefly to the secondary and tertiary strata, parti- 
cularly in the neighbourhood of Paris, the Isle of Wight, and the beds round London. 
The shells which are found in the different beds in these strata, possess distinct cha- 
racters ; some being of fresh water, and some of marine origin* ; it is hence in- 
ferred, that these portions of the surfaces have been alternately submerged under 
a lake, and under the sea, and that several of such changes have happened. The 
remains of land animals have been also fouud in these strata, washed in, probably, 
by rivers or by other causes. The comparative rarity of the remains of land ani- 
mals may he accounted for, from the land of that period being probably now under 
the sea ; and also, the remains of animals dying on the land are less likely to be 
preserved than those dying in the water, which latter would become immediately 
imbedded or buried in the deposit of new strata then forming. It may here be 
observed, that all regular strata or beds are considered to have been formed by 
deposition at the bottom of a sea, lake, or estuary, from the detritus or decomposi- 
tion of rocks previously existing. The quantity of shells and impressions of fish 
establish this in the beds in which they are found, and hence the same is inferred of 
others ; but there are beds or strata, as gneis, mica slate, clay slate, which are of a 
doubtful origin ; since their stratified structure might be given hv an excess of mica 
or other cause ; and from the uninterrupted transition which, as has been mentioned, 
is found in all species of rocks. 
Besides the beds of diluvium, gravel, and pebbles, it has been mentioned, that 
boulders or round masses of granite, greenstone, &c. are frequently found on the 
surface, at great distances from any mass of similar rock, from which they may be 
supposed to be derived. — The mode in which this may have happened is not well 
accounted .for ; by some geologists they are considered as having been brought U> 
their present position by a great torrent, and they have traced them to lie in 
a particular direction from the mountains from which they suppose them to have 
been detached ; by other geologists they are considered to he the more durable 
portions of a rock w hich has covered the surface. 
Meteoric stones are also found lying on the surface, and, as has been mentioned, 
often resemble greenstone ^ many explanations have been offered, attempting to ac- 
count for them. That most generally received, is that they are small bodies, 
wandering in space, and hence attracted by all the larger bodies or planets. If the 
ellipse in which they move be so excentric, that the curve falls within the limit of 
the crust of the plane, which is one of its foci, these small bodies will come m 
contact with, or fall on its surface: on the other hand, should the distance trout* 
the focus to the curve be greater than the radius of the planet but only by a smalt 
quantity, they will be carried through the upper atmosphere with great velocity, 
and give the appearance of balls of tire. Another idea, is their being formed 1a the 
atmosphere, from the various gases which may be supposed to be accuimilated in i 
from volcanoes, &c. &c. suddenly combining by means of the electric fluid. But were 
this the case, the stone, in falling, would be influenced by the earth s rotatory motion. 
The flints, which are accumulated in great quantities in some parts of England, 
and in other chalk countries, are considered to have been derived from of chalk, 
which have disintegrated, and disappeared ; this is sufficiently established, since t ese 
flints are quite similar to those found in chalk ; but the nodules of ^lex whah aie 
found in beds lying above the chalk, cannot well be ® u l^ s 5* in thesame 
derivation ; and some geologists consider them as pro ■ y nodules or 
manner as siliceous tufa, from springs having silex in solution. Thes *»»**«“ 
pebbles are found in beds of gravel or clay, and are generally 
depth from their surface in concentric nngs, probably fiom decompositio goi g 
* The general characters o-iven distinguishing these shells, is the fresh water being 
i tie general cnai aciers gi g considered salt water shells, as is found to 
much thinner, and more delicate, tnan rnose coiuhug , , . • • chills of 
be the case it. ’the shells of the preset.! lake, and : *»*; ^Zfrv a! the 
intermediate character, are considered to have beet were sufficiently defined to 
month of a great river/ Tl.at.be character of the shells teeresnBcmntl^ dettn eato 
warrant the deduction mentioned, was at first much q P > 
Conchology has been more studied, it appears to he aduai 
