ple, but all-important lesson in mineralogy. A second lesson teaches us that, out of nearly sixty pure mineral substances which are known, six of them, although seldom obtained in a separate state, are found so largely combined with this same oxygen as to form, in this compound state, nineteen twentieths of all the rocks and earths which are known. Thus ten twentieths of the inorganic parts of our globe are composed of oxygen; six mineral substances go to make up nine twentieths more; and the remaining one twentieth is composed of other minerals. 5. The six mineral substances, or mineral bases, to which we have alluded, have been named silicon, calcium, aluminum, magnesium, potassium, and sodium. Thus silicon unites with oxygen in certain proportions to form the well-known and abundant flinty or quartz rock. When quartz is broken down into fine grains, and consolidated or cemented with oxyd of iron, it forms sandstone rock; and, in the form of finely-powdered sand, it is an important ingredient in the soil we cultivate. Calcium and oxygen form lime; and when this is united with carbonic acid, the result is limestone rock, which is also an ingredient of our best soils. Similar combinations of the other mineral bases with oxygen form alumina, magnesia, and soda, which also enter to a considerable extent into the composition of the rocky and earthy portions of the globe. 6. The most abundant of the simple minerals, or rocks, as they are generally called, which are formed chiefly by the simple union of oxygen with the six mineral substances mentioned, but in some instances by additional combinations, are quartz, feldspar, limestone, hornblende, mica, talc, and serpentine; and these are distinguished and described by their color, and their several degrees of lustre, transparency, specific gravity, hardness, fracture, tenacity, taste when soluble, and odor when rubbed. 7. Of these minerals, quartz, which enters largely into the compound minerals or rocks, constitutes by itself nearly one · half of the crust of the earth. Pure quartz, which is crystallized silica, scratches glass with facility, and is next to the diamond in hardness. Flint and rock-crystal are well known forms of this mineral, but it occurs in numerous other varieties; and when colored by iron, manganese, chrome, and other foreign substances, it produces many valuable gems or precious stones, such as opal, jasper, amethyst, agates, and carnelians. The sand which is used in making mortar and glass is mostly quartz; and in what is called silex this mineral forms the hard, flinty covering of the grasses. 8. Feldspar, or fieldspar, which contains a large proportion of alumina, the basis of clay, composes about one tenth of the crust of the globe. It is of various colors, is not so hard as quartz, and is less glassy in appearance. It is used extensively in the manufacture of porcelain. Common clay is impure decomposed feldspar. 9. Limestone, forming about one seventh of the crust of the earth, presents numerous varieties-from the common chalk, cavern stalactites, and coarse limestone rock, to the beautiful crystalline spars and the finest marble. 10. Hornblende, a tough mineral, as implied in the name it bears, constitutes a large part of the rocks of volcanic origin and some of the older slate rocks. It forms about one fifteenth of the crust of the earth. One of its varieties is the remarkable asbestus, whose slender fibres may be woven into cloth which will be incombustible. 11. Mica, often improperly called isinglass, is a soft mineral, usually of a light green color, and is about as abundant as hornblende. Thin plates of it are often used for lanterns and stove windows. 12. Talc resembles mica, but is softer, and may be easily cut with a knife. Steatite, or soap-stone, one of its varieties, is extensively used for fireplaces and stove linings. 13. Serpentine, which is of various colors, is harder than limestone. Its finer varieties, which admit a high polish, are an elegant substitute for marble. 14. Gypsum, or "plaster of Paris," rock-salt, and coal, complete the list of minerals which form any considerable portion of the earth's crust. LESSON XVI.-COMPOUND MINERALS. 1. GRANITE, which forms so large a proportion of the primary rocks, is a crystalline aggregate of quartz, feldspar, and mica. It is a very hard and durable rock, and is much used in building and for pavements. Granite seems to be the general foundation-stone or underpinning of the other rocks, and it is also found as high as the summit of Mount Blanc. 2. Granite is abundant in New England. The most celebrated quarries are at Quincy, Mass. The Quincy granite, however, is not properly a granite, but a syenite, in which hornblende takes the place of mica. Bunker Hill Monument, the Astor House in New York City, and the drydocks at the Charlestown and Gosport Navy-yards, are constructed of this rock. Granite is also found abundantly, and of the finest quality, in Virginia, Georgia, and other states. 3. There is an unstratified igneous rock, called porphyry, which is of a reddish color, and contains crystals of feldspar. Another compound rock is called pudding-stone. It is a conglomerate of rounded pebbles cemented together by finegrained sandy paste. When cut and polished, it resembles in appearance a slice of plum-pudding, and is much used for ornamental purposes. 4. Amygdaloid is a rock containing almond-shaped cavities. These cavities have been formed by the escape of gases as the rock cooled down from a melted state. The rock itself is evidently a kind of solidified lava, and the cavities have been subsequently filled with some mineral matter, as quartz, lime, or agate. 5. Breccia is composed of angular fragments which once constituted other rocks. It differs from pudding-stone in not having the fragments worn into the form of pebbles. The Potomac marble, of which fine specimens are seen in the old national Capitol at Washington, is a kind of breccia.1 Brecciated2 marble from Vermont and Tennessee have been extensively used in the interior of the new United States Capitol. The composition of these rocks has been presented in the following recipes for GEOLOGICAL COOKERY: 6. 7. 8.. To make Granite. Of feldspar and quartz a large quantity take, If with bishops and lords in the state-room you dine, To make Porphyry. Let silex and argil be well kneaded down, To vary your dishes, and shun any waste, 9. 10. 11. To make Amygdaloid. Take a mountain of trap, somewhat softish and green, And the mass in a trice will be amygdaloidal. To make a good Breccia. Break your rocks in sharp fragments, preserving the angles; Then let your white batter be well filtered through, To make a coarser Breccia. For a breccia more coarse you may vary your matter; 1 BRE¤'-CIA (pronounced Brek'-sha). 2 BREC'-CIA-TED (pronounced Brek'-she-at-ed). LESSON XVII.-BRIEF EXTRACTS. 1. "GEOLOGY, in the magnitude and sublimity of the objects of which it treats, undoubtedly ranks next to astronomy in the scale of the sciences."-SIR J. F. W. HERSCHEL. 2. "Every rock in the desert, every boulder on the plain, every pebble by the brook side, every grain of sand on the sea-shore, is replete with lessons of wisdom to the mind that is fitted to receive and comprehend their sublime import." 3. "The very ground on which we tread, and the mountains which surround us, may be regarded as vast tumuli, in which the organic remains of a former world are enshrined." -PARKINSON. 4. "To the natural philosopher the rocks and the mountains are the grand monuments of nature, on which is inscribed the history of the physical revolutions of the globe, which took place in periods incalculably remote, and long antecedent to the creation of the human race. They present to his mind a succession of events, each so vast as to be beyond his finite comprehension; ages of tranquillity, with lands and seas teeming with life and happiness, succeeded by periods in which the earthquake and the volcano spread universal ruin and destruction; and they teach him that all these awful changes bear the impress of the ALMIGHTY hand, and were subservient to the eternal purpose of rendering this planet the fit abode of MAN during his mortal pilgrimage." -MANTELL. LESSON XVIII.-CONCLUDING REMARKS. [From the conclusion of MANTELL's Wonders of Geology.] 1. WITH these remarks, I conclude this attempt to combine a general view of geological phenomena with a familiar exposition of the inductions by which the leading principles of the science have been established. And if I have succeeded in explaining in a satisfactory manner how, by laborious and patient investigation, and the successful application of other branches of natural philosophy, the wonders of geology have been revealed-if I have removed but from one intelligent mind any prejudice against scientific inquiries which may have been excited by those who have neither the relish nor the capacity for philosophical pursuits-if I have been so fortunate as to kindle in the hearts of others that intense and enduring love and admiration of natural knowledge which I feel in my own, or have illuminated the mental vision with that intellectual light which, once kindled, can never be extinguished, and which reveals to the soul the beauty, and wisdom, and harmony of the works of the Eternal, I shall indeed rejoice, for then my exertions will not have been in vain. And although my humble name may be soon forgotten, and all record of my labors be effaced, yet the influence of that knowledge, however feeble it may be, which has emanated from my researches, will remain forever, and, by conducting to new and inexhaustible fields of inquiry, prove a never-failing source of the most pure and elevated gratification. 2. It is indeed the peculiar charm and privilege of natural philosophy that it Can so inform The mind that is within us-so impress Nor greetings where no kindness is, nor all The dreary intercourse of common life, Can e'er prevail against us, or disturb Our cheerful faith, that all which we behold Is full of blessings!-WORDSWORTH. For to one imbued with a taste for natural science, Nature unfolds "her hoarded poetry and her hidden spells;" for him there is a voice in the winds and a language in the waves, and he is |