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and crystallographic laws as the rocks of the earth, and have afforded no new element or principle of any kind.
The moon presents to the telescope a surface covered with the craters of volcanoes, having forms that are well illustrated by some of the earth's volcanoes, although of immense size. The principles exemplified on the earth are but repeated in her satellite.
Thus from gravitation, light, meteorites, and the earth's satellite, we learn that there is oneness of law through space. The elements may differ in different systems, but it is a difference such as exists among known elements, and could give us no new fundamental laws. New crystalline forms might be found in the depths of space, but the laws of crystallography would be the same that are displayed before us among the crystals of the earth. A text-book on Crystallography, Physics, or Celestial Mechanics, printed in one of our printing-offices, would serve for the universe.
The earth, therefore, although but an atom in immensity, is immensity itself in its revelations of truth; and science, though gathered from one small sphere, is the deciphered law of all spheres.
It is well to have the mind deeply imbued with this thought before entering upon the study of the earth. It gives grandeur to science and dignity to man, and will help the geologist to apprehend the loftier characteristics of the last of the geological ages.Pp. 3, 4.
These are long extracts, considering the few pages to which our article must be limited, but the reader who has not ready access to the work itself will not regret their insertion. They are taken from the author's "Introduction," and every one will agree that they furnish excellent ground of hope for a satisfactory treatment of the subject in the body of the work.
The author's division of his subject is peculiar and original. His work treats of the science under the five heads or "Parts," PHYSIOGRAPHIC GEOLOGY, LITHOLOGICAL GEOLOGY, HISTORICAL GEOLOGY, DYNAMICAL GEOLOGY, and COSMOGONY. Under the treatment of so able a hand this arrangement answers well, though at first view it seems defective, especially for a work to be put into the hands of students. A very natural arrangement for a text-book on geology is that adopted in the "Elements of Geology" by Gray and Adams, which, for quite a number of years, has been the chief text-book in this branch of science used in American seminaries of learning. The essential peculiarity of it is that a considerable space, at the very first, is devoted to the discussion of "Geological Agencies," that is, the agents by which the earth has been brought
to its present condition. This to the student is of great importance as a preparation for the task he has prescribed for himself. Few persons that have not had their attention called to the wonderful effects produced by those agencies, with special reference to this science, are aware of the great geological changes that are almost everywhere constantly in progress even before our eyes. They have indeed seen some change in the river's bank or channel, or in the filling up of a harbor or watercourse, or the slide that has come down the side of a mountain, and have read of similar occurrences elsewhere, and of the results of earthquakes and volcanic action; but still, without a systematic examination very few are capable of appreciating the mighty changes which have been produced by these agencies during the few thousand years denominated the historic period.
This preparation, in some form, for the study of the grand subject, seems to be essential for the student; and if before entering upon the study of this work he can find time to read only a few chapters of the first volume of "Lyell's Principles," he will find it a great advantage.
This point, on a smaller scale, is recognized by all writers on geology, by introducing somewhere in their works a chapter treating specially of the general classification of animals and plants. Our author occupies twenty pages (pp. 147–167) in this way. This in fact is absolutely necessary for a proper understanding of the subject.
The name Physiographic Geology, which the author has chosen for the first part of the work, is perhaps sufficiently expressive of the topics discussed in it. These are essentially the same as we find treated of in works on Physical Geography. They are necessarily included in any proper description of the earth, but we do not recollect to have seen them so formally introduced in any other work on geology. Many of the points presented are the same substantially as are found in other authors, but some are original and striking:
If a globe be cut through the center by a plane intersecting the meridian of 175° E. at the parallel of 40° N., one of the hemispheres thus made, the northern, will contain nearly all the land of the globe, and the other be almost wholly water...
The pole of the land-hemisphere in this map is the western half of the British Channel; and if this point on a common globe be
placed in the zenith, under the brass meridian, the horizon-circle will then mark the division between the two hemispheres.-Pp. 10, 11.
The author might have added, the pole of this land-hemisphere, being thus nearly midway between London and Paris, may be taken as the great center of civilization and of finance for the whole globe.
In this part of the work the grand features of the earth's surface, its continents and oceans, its mountain ranges and elevated plateaus, its rivers, lakes, and islands, its oceanic and atmospheric currents, are well but of course briefly described. The continents are only two in number, the eastern and western-the "orient" and the "occident"-Australia being considered as making a part of the "orient," as is evidently proper. The eastern continent, even including Australia as a part of it, does not extend as far south as the western, but has a much greater breadth in its northern part, and its southern bifid prolongations are separated by the Indian Ocean.
The highest mountains of the globe are in the torrid zone; and nearly within the same limits the waters in east and west lines almost divide both the orient and occident, there being required for the purpose only thirty-seven miles of canal at the Isthinus of Darien, and seventy miles at the Isthmus of Suez.
There are three great oceanic basins, the Atlantic, the Indian, and the Pacific. The first two have but few islands, but in the Pacific there are no less than six hundred and seventy-five. Many of these are in clusters in mid-ocean, and may be considered the tops of sub-oceanic mountains.
Climate too comes in for consideration, and many interesting and important facts are presented.
The laws of the winds are the basis of the distribution of sterility and fertility:
1. The warm tropical winds, or trades, are moist winds; and blowing against cooler land, or meeting cooler currents of air, they drop the moisture in rain or snow. Consequently, the side of the continent or of an island struck by them—that is, the eastern-is the moist side.
2. The cool extra-tropical winds from the westward and high latitudes are only moderately moist, (for the capacity for moisture depends on the temperature,) blowing against a coast, and bending toward the equator, they become warmer, and continue to take
up more moisture as they heat up; and hence they are drying winds. Consequently, the side of a continent struck by these westerly currents-that is, the western-is the drier side.
There is, therefore, double reason for the difference in moisture between the opposite sides of a continent.
Consequently, the annual amount of rain falling in tropical South America is 116 inches, while on the opposite side of the Atlantic it is 76 inches. In the temperate zone of the United States, east of the Mississippi, the average fall is about 44 inches; in Europe, only 32....
It is well for America that her mountains stand in the far west, instead of on her eastern borders to intercept the atmospheric moisture and pour it immediately back into the ocean. The waters of the great Gulf of Mexico (which has almost the area of the United States east of the Mississippi) and those of the Mediterranean are a provision against drought for the continents adjoining. It is bad for Africa that her loftiest mountains are on her eastern border.-Pp. 46, 47.
One peculiarity of our American rivers he omits to mention. Nearly all our rivers are subject to greater variations in the quantity of water flowing in them at different seasons than European rivers are. This is greatly to the disadvantage of the interests of navigation on them. The rivers of Europe are indeed subject to the same irregularities, but in less degree. The reason is found in the fact that the mountains of Europe, where several of the larger rivers have their origin, are covered the whole year with ice and snow, which are rapidly melted by the heat of summer, and thus the flow of water in the different seasons is in a great degree equalized.
The Second Part of the work before us, devoted to Lithological Geology, contains a very full description of all the various kinds of rocks which form the crust of our globe, or all that part of it to which we have access; while the Fourth Part, or Dynamical Geology, treats of the causes of events in the earth's geological progress.
These two great branches of the general subject are certainly to some extent distinct from each other, and yet it is a question whether there is anything to be gained by treating of them separately. In another connection he says: "Geology is sometimes defined as the science of the structure of the earth. But the ideas of structure and origin of structure are inseparably connected and in all geological investigations they go together."-P. 4. This is indeed said of the structure of the earth itself, but it is FOURTH SERIES, VOL. XVII.-25
equally true of the structure of the strata that form the earth's crust, to which the teachings of the science are chiefly limited. The difficulty of separating a description of the rocks from any discussion of the forces or agents by which they have been formed, becomes very apparent when an attempt is made to describe certain kinds of rocks, as those called metamorphic. To convey a clear idea of the peculiar characteristics of these rocks, the very best method is to describe the mode in which it is believed they have been formed; first, as sedimentary deposits, with or without organic remains, but afterward altered or metamorphosed more or less by the action of heat, obliterating the organic remains, if any, and producing partial crystallization. The author himself falls into this method in his first sentence describing these rocks. (See page 74, and also page 704.)
But while saying this, as in our belief strictly true, we hasten to say that we, in reality, have no quarrel with the author's arrangement. Such a science as geology admits of various. arrangements of its details, each having its own advantages and disadvantages. He has presented the subject very admirably for the use of such as are systematically seeking a thorough knowledge of it; but if occasionally the persevering student, in his efforts to master "Lithological Geology," finds it a little tedious, he may be excused if he is disposed to attribute it in. part to the peculiar arrangement of the different parts of the work.
But the charm of this great work is found more especially in the Third Part, which treats of "Historical Geology." Here it is that the advantage of the author's method is made to appear so plainly.
We have heretofore seen, when we come to recognize the fact that the earth has been brought to its present condition by the regular operation of natural causes, we are then prepared to understand that there has been a regular progress and development in its affairs; and this progress or development, if we can mark its varied steps, is as much a matter of historical inquiry as are the progressive events in the affairs of the human race. But while there has been an unceasing flow, a continual progress, in the changes by which the present condition of the earth's crust has been produced, it is reasonable