2 GEOLOGICAL SURVEY 
stitute the greater portion of the materials included in this thickness. Of these, eight are non- 
metallic substances : 
Oxygen, Nitrogen, Sulphur, Fluorine, 
Hydrogen, Carbon, Chlorine, Phosphorus. 
Six are metallic bases of the alkalies and earths: 
Silicium Potassium, Magnesium, 
Aluminium, Sodium, Calcium. 
And two are metallic Oxides: 
Tron, | Manganese. 
Such is the chemical relation existing between these substances, that, with a few exceptions, they 
rarely occur in nature in their simple and uncombined state. Oxygen, for instance, by its chemical 
union with the bases of the alkalies and earths, and with Hydrogen and Carbon, produces the well 
known substances, Silica, Alumina, Potash, Soda, Magnesia, Lime, Water, and Carbonic Acid.— 
These again, by their combination with each other, give rise to a few minerals, which, by their 
aggregation, make up by far the greater portion of all rocks. Thus, 
Silica alone forms - - - . - - - Quartz ; 
Silica, alumina, potash, or soda, form - - - - Feldspar ; 
Silica, alumina, potash and iron, - - - - - Mica; 
Silica, magnesia and iron, - - - - - - Talc; 
Silica, magnesia, lime, alumina and iron, — - - - Hornblende ; 
Silica, alumina, lime and iron, - - - - - Argillite ; 
Lime and carbonic acid, —- - - - . - Limestone. 
Numerous other minerals are found embedded in rocks, and entering into their composition ; but 
of the mass, they generally form but a small proportion, compared with these. 
The first object of the student of Geology should, of course, be to make himself acquainted with 
these minerals; and although it is not easy to give correct ideas of minerals by mere ordinary 
description, yet these are so widely distributed, so abundant, and so easily recognized, that they 
offer but little difficulty. 
Quartz, which in this State is called white flint, is readily known by its glassy appearance, 
uneven fracture, and great hardness. It presents a variety of colors, and is esteemed for gems, 
under the names of amethyst, agate, cornelian, &c. It constitutes nearly one half the mass of all 
known rocks. 
Feldspar is distinguished from quartz by its inferior hardness and its distinct cleavage. It has a 
high lustre, is generally semi-opaque, and is of a white gray or flesh color. It constitutes nearly 
one-tenth of the earth’s crust. ; 
Mica is known by the thin elastic plates into which it is readily divided. Its bright shining 
metallic lustre is a fruitful source of disappointment to unskilful searchers after gold and silver. It 
is called, in this country, isinglass. 
Tale is quite soft and greasy to the touch. From mica, which it sometimes resembles, it is dis- 
tinguished by the want of elasticity, and by its unctuous touch. It is sometimes known by the name 
of French chalk: its colors are white and green. 
Hornblende, in its most common form, presents a confused erystaline structure, and dark green 
color, approaching black. The rocks composed of this mineral are exceedingly tough, and yield 
