Chat. I.
GEOLOGY.
635
Diallage or Serpentine may be considered as a hydrated subsilicate of magnesia; its com-pounds are in the third column. It should be observed that the felspar and hornblende arein equal quantities in the greenstone; the felspar and hypersthene in equal parts incolumn two; and in the third column the proportions are two-thirds of common felsparand one-third of diallage.
Silica -
No. 1.
- 5-1*86
.
No. 2.
59 T 4
.
No. 3.58-42
Alumina
- 1556
-
10*59
-
13*86
Potash
6-83
.
6-83
-
9-10
Lime - - -
7*29
-
113
4-87
Magnesia
9*39
-
7 00
-
813
Oxide of iron -
4 03
-
12*62
.
2-00
Oxide of manganese
Fluoric acid
Water -
on
- 0 75
0-20
1-06
Water .—This important element occupies about three-fourths of the whole surface of theglobe, and geological researches having dispelled the many fanciful theories that existed onthis interesting subject, it is generally agreed that within its depths the various mattersand crystallised bodies which now constitute the dry land have been precipitated, fromthe disintegration of other lands no longer existing. Of the period of time during whichthese changes were going on it would be useless to speculate; the “Medals of Creation"will enable us to class in some measure the great transitions, but they afford us no fixeddates.
At all temperatures above 32° water remains in a liquid state; when cooled below this itis congealed, and becomes solid, forming prismatic crystals, which lie across each other atangles of 60° and 120°. During the formation of ice the mass is increased in bulk a ninthpart, and its expansive powers become greater, which, acting mechanically upon rocks or otherearthy matter, breaks them up into smaller masses, and it thus becomes a powerful agent inthe destruction of cliffs, or even mountains, though by slow degrees, and by successiveoperations. When the temperature of water is raised to 212°, it passes off into steam,though it is found in a state of vapour at all temperatures under pressure.
Tlie atmosphere contains a large quantity of water, and it may be called the greatreceptacle of that dement; all the moisture carried away by evaporation from the oceanand land enters the atmosphere as vapour, where it floats, until, being driven against higherland, it is converted into water in the form of rain or snow by condensation, and againdrained off to the ocean.
Water in its ordinary state is frequently found to contain foreign matter, which rendersit totally unfit for domestic uses. Rain water, if collected with care, is the most pure, butin it there are small quantities of carbonic acid and atmospheric air, as well as appreciabletraces of vegetable and animal matter, which occasion it, when kept for a length of time, tobecome putrid.
Water is sometimes designated hard and soft, and these states may be ascertained bydropping into it a solution of soap dissolved in alcohol, which will produce at once a milkyeffect, if it contains any earthy or metallic salts, the presence of which constitutes itshardness, and throw them down in a flocculent precipitate.
There are five great seas or basins from whence the earth derives the supply of moistureso necessary for its fertility, and the existence of its various inhabitants.
The Pacific Ocean is of vast extent, and derives its name from the quiet of its waters,particularly between 10° and 30° of north latitude, where it is almost always calm. Thissea extends 3700 leagues from east to west, and 2700 in the other direction. The coastsof America and Asia are its boundaries, and in the midst of this world of waters rise upnumerous islands and coral reefs, which have their foundation at immense depths, andpresent a perpendicular face from the bottom to their surface.
The Atlantic Ocean , which receives the waters of some of the largest rivers of the world,is not more than half the area of the Pacific.
The Indian Ocean is in length and breadth about 15C0 leagues.
The Arctic Ocean surrounds the north pole, and is a vast circular basin, which, by meansof two channels, connects the Pacific and the Atlantic .
The Antarctic unites the Indian Ocean and the Pacific.
The Mediterranean is 2300 miles in length, and 650 in breadth ; the Straits of Gibraltar uniting it with the Atlantic , and the Dardanelles with the Black Sea , beyond which is theSea of Azoph : still further lies the Caspian, which has apparently no communication withthe ocean.
The Baltic Sea is 1200 miles in length, and nearly 100 in breadth, and unites with theGerman Ocean.
The water in the northern and southern hemispheres differs considerably in quantity • inthe former the proportions between land and water are as 72 to 100, and in the latter only