Page:Popular Science Monthly Volume 4.djvu/132

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Workshop Appliances; including Descriptions of the Gauging and Measuring Instruments, the Hand Cutting-tools, Lathes, Drilling, Planing, and other Machine-tools used by Engineers. By C. P. B. Shelley, Civil Engineer. 209 Illustrations, 312 pages. Price, $1.50. D. Appleton & Co.

this is a hand-book of tools and their uses, compendious in form, and copiously illustrated, which will be of great value to young artisans and mechanics, whether working in wood or metal. There is no end to machines for reshaping the materials of Nature, and inventors are constantly adding to them; but the fundamental tools for producing mechanical effects, with their resources of variation, fall into a few classes, and their modes of action are capable of explanation within a narrow space. It is the variation and recombination of comparatively a few implements that are constantly coming before us in the form of complex and obscurely acting contrivances. Two objects are to be gained by the use of tools: 1. The production of given mechanical effects; and, 2. Accuracy in the processes. Both of these objects are now attained by mechanics with a remarkable degree of perfection. Mr. Shelley describes these in clear and simple language, which, with his excellent illustrations, makes the subject quite intelligible to ordinary readers. Besides its value as a practical hand-book to the working mechanic, this little volume will have great interest for those who wish to understand how the wonders of modern construction are executed.


Yosemite Valley of Glacial Origin.—In the summer of 1872, Prof. Joseph Le Conte, of the University of California, with several students of the institution, visited the Yosemite and the mountains contiguous, and carefully examined the results of the glacial action which were everywhere apparent. His conclusions were stated in an able paper, published in the American Journal of Science for May. The Yosemite Valley, he thinks, was once filled to the brim with a great glacier. In this he differs from Prof. Whitney, who in his guide-book expresses the opinion that there is no evidence that such a glacier existed.

Prof. Le Conte observes that glaciated forms are unmistakably observable at many points on the walls of the valley, and in some places even to the brim. In the contour of the walls of the valley, their rounded form, where the rock is hard, standing unbroken and without débris at the base, he finds proofs of glacial erosion. On the north side of the valley, every projecting shoulder is thus rounded, and in some cases the smoothness is so complete, even at a considerable height, that the rocks glisten in the sunshine. Where the rocks are soft, and on the southern side of the valley, which is in shadow, frost and other agencies have done their work of disintegration. The surfaces are broken, and the débris lies at the base.

The bed-rock of the valley is covered with mounds of bowlders and sand, which are terminal moraines of glaciers, and by stratified lake-deposits, the lakes having been formed by the glacial mounds obstructing the flow of waters.

But it was from the higher elevations that the wonderful features of the glacial erosion were most distinctly observed. "From the edge of the rim of Little Yosemite," says the author, "we had a magnificent bird's-eye view of the wonderful domelike form of nearly all the prominent points about this valley, and their striking resemblance to glaciated forms cannot be overlooked. The whole surface of the country is moutonné on a huge scale. If so, then the greater domes about the Yosemite have been formed in a similar manner. If so, then the whole surface of this region, with its greater and smaller domes, has been moulded beneath a universal ice-sheet, which moved on with steady current, careless of domes."

This great ice-sheet preceded the separate glaciers which completed the erosion of the valleys of which Yosemite is one, and the scattered snow-fields which were discovered by Mr. Muir, of the expedition, are feeble remains of the old glaciers. In the opinion of Prof. Whitney, the Yosemite was formed by a sudden engulfment of a portion of the sierras, but Prof. Le Conte observes that Yosemite is not unique in