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THE POPULAR SCIENCE MONTHLY.

identical species as belonging to a former Arctogæal fauna. The action of the steady increase of cold which characterized the gradual inauguration of the Ice period would have been to drive the insects southward and mix the Arctogæal with the then existing 'indigenous' southern species. The summers of the middle Glacial epoch probably afforded no opportunity for the existence of Noctuidæ throughout the Northern States. On the decline of the Glacial epoch, and with a steady increase of warmth (still continuing), the species would progress northward again. We may regard such a species as Fidonia fimitaria G. & R., found in Texas, as an outlying colony of F. fasciolaria forced southward and retained by local influences, and possibly having submitted to the modification which enables us at this day to separate the two forms. During the Pliocene, the common ancestor of the two forms may have been different from either. During the Pleistocene, Holocene, and Recent periods, we must consider such species as Hadena arctica to have preserved their identity, while many may have perished or submitted to modifications, and these latter may be represented by the closely-allied species of the two faunæ. The Glacial epoch may then supersede the "Atlantis" of those entomologists who looked for a geographical connection in former times to account for the existence of identical or representative species on the two continents."

 

The Pottery of the Mound-Builders.—Prof. E. T. Cox, having examined a great many specimens of potteries of the ancient mound-builders in the Western States, has never been able to find any evidence of their having been hardened by fire, or even sun-baked. The material employed is a mixture of river-mud and, most generally, pulverized mussel-shells, united in such proportions as to make a cement which hardens in the air, or on being exposed to moisture, like the concrete of the ancient Romans; hence this ancient "pottery" is in fact a sort of artificial stone. In chemical composition it agrees very closely with the concrete made of ordinary cement-stones. These facts lead to the conclusion that the art of manufacturing concrete, or artificial stone, did not originate solely with the ancient Romans, but that it was alike understood by the earliest inhabitants of America. As regards the mechanical processes followed by these ancient artisans, Prof. Cox says: "Though it is my opinion that the so-called pottery of the mound builders was fashioned by hand, without the use of a lathe, yet I am convinced that the ancient pottery of Peru, and other South American states, was largely made of pieces formed by pressing the cement into moulds, and these pieces were subsequently united together to form the entire vessel. The lines of union are usually covered by a band, or some grotesque image. The numerous tubercles and other raised ornaments, which cover the surfaces of jugs, vases, etc., could only have been formed in this way. I do not, however, find any pottery of the mound-builders that would lead to the belief that their skill went so far as to enable them to mould it in parts, or to fashion it in any other way than by the hands."

 

A Primitive Fort.—One of the most remarkable works left by the mound-builders is a stone fort in Clarke County, Indiana. As described by Prof. E. T. Cox, this fort stands upon the terminal point of a high ridge, which is washed on its south side by the Ohio River, and on the north by Fourteen-Mile Creek. The point of the ridge is pear-shaped, and the fortification includes from eight to ten acres. The highest point at the stem of the pear is 280 feet above the Ohio, and is only 10 to 20 feet broad, presenting almost a perpendicular wall to the river. A natural wall of Niagara limestone furnishes complete protection against the approach of an enemy at the upper part of the fort, with the exception of a short gap on the creek-side, extending from the upper point southward for about 100 paces. This break in the natural wall is protected by an artificial wall 75 feet in height, made by laying up loose stone, mason-fashion, but without mortar. The base, for 65 feet in height, follows the slope of the hill-side, and then rises 10 feet vertically. Around the southern terminus of the point there is an artificial stone-wall 10 feet high, which connects the two natural walls of Niagara