Royal Institution. 393 
fire might be attributed to the existence of the earths in 
their metallic state in the interior, acted on by air and 
water, and thus supplying fuel, and that the reproduc- 
tion of these metals might be owing to internal electri- 
cal currents. In the Neptunian hypothesis, water is the 
general solvent, and sapplies the place of fire in the 
Plutonian ; and our continents are supposed to be derived 
from a fluid chaos, the primary rocks by crystallization 
and deposition, and the secondary by a simple deposition 
at a later period, after the sea was stocked with inhabitants. 
Beside these two, many others have been resorted to. Leib- 
nitz and Whiston, for instance, imagined a comet to have 
been concerned in producing the present appearance of 
things, by elevating the ocean, inundating the continents, 
and by heating its waters giving them new solvent powers. 
Mr. Davy pointed ont two grand circumstances con- 
nected with this inquiry; Ist, Alterations produced in se- 
condary rocks by causes acting from above, such as the 
opening of valleys, the sweeping away of strata, &c. with- 
out the parallelism of the remaining strata being altered.— 
2dly, The derangement of the primary rocks by causes ap- 
parently acting trom below. He asserted that more than 
one system of causes was necessary to account for all the 
phenomena, and that the practice of assigning them all to 
ne was faulty: be advanced several illustrative instances 
jn which unity of effect is the result of a variety of causes, 
Mr. Davy recommended to those who wished to become 
acquainted with geology, the examination of geological col- 
lections, and the perusal of geological writings, particu- 
Jarly of those enlightened observers, De Saussure, Dolomieu, 
Humboldt, and Jameson. 
He stated that the science, independent of the healthy 
employment it gives to the mind, is of great importance in 
a practical point of view; that it very nearly concerns the 
miner, engineer, and drainer, and even the farmer and 
architect—that it discloses a variety of indications highly 
useful in their respective pursuits:—to the miner, the rocks 
containing metallic veins and coals; to the-engineer, the 
-association of bard rocks with soft; to the drainer, the in- 
_tersection of a country by hard dykes, or veins impermeable 
to water; to the farmer, the best places for finding lime- 
stone, marl, and clay; and to the architect, the most dura- 
ble stones for buildings : and he memtioned several instances 
of the, serious evils arising froma want of yeological know- 
ledge. 
The person who js attached to geologiogl inquiries,” says 
: Mr. Davy, 
