Royal Institution. 397 
in beds or veins: these’ rocks are much move abundant in 
metalic ores than the primary rocks; they are not so pro- 
per for architectural purposes, being liable to decomposi-. 
tion; but when decomposed they afford clays and earths, 
which form the basis of the finest porcelain, and which are 
applicable to other purposes in the arts. In this family no 
organic remains have as yet been found. 
The second family of the secondary rocks contains the 
impressions of marine exuvice, less crystalline matter than 
the first family, and fragments in greater abundance: it is 
composed of the argillaceous and ‘siliceous schists, the 
schistose porphyries, trapps, grawackes and breccias. The 
mechanical elements of all these rocks, independent of the 
fragmeuts they contain, are principally feldspar, quartz, 
hornblende and chlorite; feldspar serving ‘as a cement to 
connect the others together. - The rocks ‘of ‘this family are 
variously associated with each other, and ‘sometimes with 
limestone ; the position of their(strata! is irtegtilar, it’ is sel- 
dom horizontal or vertical; but generally more or less in-. 
clined. Coal, without biturmen, is peculiar to this family. 
The third family, besides marine exuviz, contains the 
impressions of fishes and vegetables, and the remains of 
quadrupeds ; it is also distinguished by a horizontal stra- 
tification, and by the uncrystalline appearance of most of 
its rocks, excepting basalts; shell limestones, sand stones, 
shales, bituminous coal, and basalts belong to this family. 
Basalts are aggregates of small crystals of hornblende and 
feldspar. L oi 
Mr. Davy was of opinion that) much remained to be 
learnt from chemistry respecting the formation of this fa- 
mily of rocks: he showed that all the phsenomena they 
present are not explicable on the supposition of the action 
of one simple cause; that fire or water alone is insufficient, 
but that their joint agencies are more agreeable to the visi- 
ble effects.-He introduced some observations on the ten- 
dency of geological speculations, when attempts are made 
to connect them with the truths of revelation. He quoted 
Lord Bacon on the occasion, and urged the separation of 
divine things from human, The ordinances of the Creator, 
he said, were not to be judged of by the fleeting opinions 
of man; their theories and their hypotheses are in con- 
tinued fluctuation, and should therefore never be blended 
with that which is divine and immutable.—The secondary 
rocks form the beds on which our fertile and cultivated soils 
are situated. They are abundant in fossil coal and in mt- 
neral veins, and they afford a number of substances ot 
pecte 
