Northern New York, and the geologists of the Natural History Survey of that state christened it accordingly from one of these localities (Fig. 22). It was burst through at some subsequent period by some of the granitic rocks now constituting the region of the Adirondacs—or, if some of their domes were already islands in the Eozoic ocean (b, Fig. 20), their massive walls have been heaved to higher altitudes by later efforts of nature, since the rocky wrappings of their flanks have been raised to inclinations which prove disturbance subsequent to their deposition. This sandstone extends southward into Pennsylvania, where, at a still later period, it was upheaved by the convulsion which brought the Alleghanies to light. Still farther south, in Virginia, Tennessee, and Alabama, this ancient sea-bottom has been brought up at intervals along the dislocations of the Appalachian range; while on the west of the Mississippi it comes up again in the highlands of Texas and Arkansas, in Eastern Missouri, and the Northwestern States, and has been broken through in the Black Hills of Dacotah by a comparatively recent protrusion of granite. From Northern New York it trends down the valley of the St. Lawrence, while in the opposite direction it crosses over to the northern shore of Lakes Huron and Superior-underlies the western portion of Superior, and spreads itself out over vast areas in Wisconsin and Minnesota, whence its main outcrop sets out for the region of McKenzie's River, on the arctic slope of the continent.

These localities and regions are but the present places of outcrop or exposure of a solidified bed of sands, which was accumulating in the bottom of the ocean at the time of which we speak. What of the beings that enjoyed the throb of life in those ancient waters? The renowned paleontologist of New York, Professor James Hall, has made us acquainted with but two or three distinct creatures

from the whole extent of the typical region of the Potsdam sandstone. These have been named Lingula prima

antiqua.

and Lingula antiqua. They are little bivalve shells belonging at the bottom of the class Brachiopoda, which is nearly the lowest class among molluscs. As desti

Fig. 23. Lingula Fig. 24. Lingula tute of the senses as an oyster, prima. they were equally incapable of locomotion, being anchored to the bottom by a fleshy stem or peduncle which issued through the hinder part of the shell, and had an internal organization which was even more rudimentary and homogeneous than that of the "bivalve,” which has become the type of insensibility and stupidity. The same little shells have been observed in Northern Michigan, in Minnesota, in Wisconsin, in Alabama, and even in the Old World, every where occupying a position in strata which were accumulated at the same time as the Potsdam sandstone. In many instances the extent to which the number of individuals was multiplied is truly amazing, while the

whole catalogue of species of mol- Fig. 25. Modern Lingulas anluscs in this sandstone scarcely

chored to a support.

reaches half a dozen. With these bivalves, in Wisconsin and Minnesota, are associated incredible numbers of trilobites. As might be expected in deposits formed under such conditions as gave rise to sands, the trilobites are found generally in a greatly damaged condition. These Northwestern cemeteries have been mainly explored by Dr. D. D. Owen, Professor James Hall, and Dr. B. F. Shumard. The writer has also had the opportunity to bring

Fig. 26. Dicellocephalus
Minnesotensis.

to light some hitherto unrecognized forms. Still other species have been made known from Texas by Dr. Shumard and Dr. F. Römer. Trilobites belong to the lower-not the lowest-part of the sub-kingdom of Articulates. The radiates and the great mass of molluscs hold inferior rank, and yet throughout the world we find these lower strata characterized by a profuseness and variety of trilobite remains which are not approached by the molluscs or the radiates. Many investigators have contributed to our knowledge of these primordial creatures, but to none are we so deeply indebted as to M. J. Barrande, who has enriched with marvelous details his great work upon the "Silurian System of Bohemia." He has traced them through the various stages of their embryonic development, and shown that they underwent metamorphoses to some extent similar to certain insects. Varying in size from a pea to a foot or more in length, they had the jointed external shell of a lobster, and could roll themselves together like a hedgehog for the purpose of passive protection. Multitudes of them are found folded in this condition (Fig. 27), intelligible witnesses of an instinctive shrinking from the death-pang, which, even in this early age, was the means employed by Providence to secure the lives of his sensitive creatures. With all except the lower forms the eyes are distinctly discernible, and

of a Trilobite (Calymene senaria) rolled up.

even in these the places for the eyes are vis- Fig. 27. Side view ible, and there is no reason to suppose they were blind. In the others the eyes are curiously compound, like those of the common house-fly. Did the reader ever examine the eyes of the domestic fly with

a hand magnifier? If not, the beautiful and perfect structure which it displays will compensate for the trouble of procuring the means to make the observation. Some scores of little lenses, arranged with the most perfect symmetry, each set in its little telescopic tube, form upon the retina of the little insect the various portions of an image of some external object. Such eyes had the trilobite (Fig. 28). It is marvelous that such delicate structures have been so

Fig. 28. The eye of a Trilobite magnified.

a. Eye of Asaphus caudatus. b. A few facets of the eye of Calymene
macrophthalmus.

perfectly preserved as in some trilobites which I have examined from the neighborhood of Dubuque, Iowa. These, however, existed in the period following the Potsdam. The trilobite was tri-lobed in two respects. Longitudinally, the oval form was divided into head, body, and tail; while in the other direction a couple of lengthwise grooves divided the animal into middle, right, and left lobes, or regions.

In this earliest scene of animalization, mollusks and radiates play comparatively an inconspicuous role. But it must be remarked that both these types of existence had been introduced. Among the molluscs we have found, besides the representatives of Brachiopods already mentioned, a few other members of the same class, and also some coiled univalves, which belong to the higher class of Gasteropods. Among the radiates we have in the Old World a few representatives from the middle of the sub-kingdom in point. of rank, while among Protozoa we find a few forms related

to sponges, with calcareous instead of horny skeletons. In the epoch immediately following this, animal life rose to a slightly higher grade, and unfolded in a great variety of subordinate types. Before the close of the Potsdam period before the deposition of the sediments which formed the limestone and marls of Cincinnati, and have given character to the far-famed "blue-grass region" of Kentuckylife had been ushered upon our globe in such richness and variety, that not only had three of the four fundamental plans of animal organization been realized, but all or nearly all the various classes of the three lower sub-kingdoms. had been fairly represented.

Many extensive regions of the Potsdam sandstone and overlying calciferous sand-rock are, nevertheless, almost, if not quite destitute of the traces of organic existence. Along the south shore of Lake Superior is a sandstone once regarded as belonging to the Potsdam, but probably, in part, of the age of the "Calciferous," in which we search in vain for any of those fossil remains so common in Minnesota. We find nothing but the imprints of soft seaweeds (Fig. 29)-things like films of jelly, which have left. their imprints upon the coarse rock, and have transmitted to us a knowledge of their existence and nature, while the traces of an army's march are obliterated by the vicissitudes of a single season.

The Lake Superior sandstone, whatever its geological age, is a formation of remarkable interest, both in its relations to the basin of the largest lake in the world, in its relations to the world-renowned copper deposits of the region, and, not less, in its relations to some of the finest scenery of the continent. The remarkable interest of this formation was first pointed out by Dr. Douglass Houghton

a name more honored and beloved among the Wolverines than any other in the lists of science.