mony with the close faunal relationship, which is shown to exist, by the few species that are named in the table. The brackish-water branchiferous species, however (as well as the pulmonate Rhytophorus priscus Meek), of the Bear River Valley series, are not only of different species from any that occur in any other strata of the Laramie Group, but a part of them are of different types also. It is also true that these brackish-water species depart more widely from living types than do any of the species of other portions of the Laramie Group. In fact, not one of the species yet found in the true brackishwater strata of the Bear River series has been identified in those of any of the other regions discussed in this paper; and the evidence of the faunal relationship of this portion of the Laramie Group with the others, which is shown in the table, is confined to pulmonate mollusks alone. It is true also that the pulmonate mollusks of the Bear River Valley series that have been identified with species found in Laramie strata in other districts are apparently confined to the Evanston coal-bearing beds that overlie the portion of the series in the Bear River Valley which contains the brackish-water types. The fact that these pulmonate species of the Evanston coal-bearing beds have also been found only in the Judith River series, which probably represents the lower or earlier portion of the Laramie Group, seems to indicate that the Bear River series of brackish-water strata is still older. But this is not necessarily the case, for there is apparently no reason why we might not expect to find those species to range through the whole Laramie series, as other species have been shown to do. In other words, from our present knowledge of the facts, it appears justifiable to regard the Judith River beds as representing the earlier and the coal-bearing beds near Evanston as the later portion of the Laramie period. It now seems probable that we must look for the cause of the differences which the branchiferous mollusks of the strata of the Bear River Valley present, from all other portions of the Laramie Group, in a difference of physical conditions probably induced by the proximity of the western shore-line of the great Laramie inland sea; conditions that induced differential changes in the aqueous mollusks, but not thus affecting the land and palustral pulmonates. In subsequent papers, it is proposed to discuss the relations of the Laramie Group with those above and beneath it; and also the relations of its molluscan types with those of other fossil, and also with those of existing forms. ART. XXX.-ON SOME DARK SHALE RECENTLY DISCOVERED BELOW THE DEVONIAN LIMESTONES, AT INDEPENDENCE, IOWA; WITH A NOTICE OF ITS FOSSILS AND DESCRIPTION OF NEW SPECIES. BY S. CALVIN, Professor of Geology, State University of Iowa. 1 The Devonian deposits of Iowa, as now known, may be roughly rep resented by the annexed diagram, in which 1 3 indicates the position of a member of the group recently discovered at Independence, consisting of dark argillaceous, with some thin beds of impure, concretionary limestone. It has been explored to a depth of 20 or 25 feet. No. 2 represents all the beds of what have been termed Devonian limestones in Iowa, and is made up largely of limestones, with associated beds of light-colored shales; estimated thickness, 150 feet. No. 3 is a bed of argillaceous shales exposed at and near Rockford, Iowa, and is referred to in this paper as the Rockford Shales. It abounds in fossils, and weathers, on exposure, into a stiff clay, that has been utilized in the manufacture of brick; observed thickness, 70 feet. Until quite recently, Nos. 2 and 3 of the above section were supposed to make up the entire thickness of Devonian rocks in Iowa. No. 2 not only varies, as already indicated, in lithological characters, but the grouping of fossils differs widely in different localities, so much so that competent geologists have referred certain exposures-for example, those at Waterloo-to the Corniferous, and others-as at Independence and Waverly-to the Hamilton. Such references of the above-named exposures will be found in the Twenty-third Report on the State Cabinet of New York, pp. 223-226; and in the same article Professors Hall and Whitfield declare the Rockford shales to be the equivalent of the New York Chemung. On the other hand, Dr. C. A. White-Geology of Iowa, 1870, vol. i, p. 187-is of opinion that all the Devonian strata of Iowa belong to a single epoch. Thus matters stood until about a year or so ago, when D. S. Deering called attention to the interesting fact that a dark shale had been exposed in working out the layers in the bottom of one of the limestone quarries near Independence. The quarrymen penetrated the shale to a considerable depth in the hope of finding coal. The shale varies somewhat lithologically, but where it presents its most characteristic features it is argillaceous, fine-grained, and highly charged with bituminous. 725 matter. In some of the beds there are numerous remains of plantsstems of Lepidodendron and Sigillaria that made up the forests of the Devonian.. The plants, however, are very imperfect; the form only is partially preserved, and that mainly by iron pyrite that replaced the original stem. The woody tissue of the plants has been converted into coal that occupies thin, irregular seams among the laminæ of pyrite. The little bands of coal vary in thickness, but none of those observed exceed a quarter of an inch. None of the plants are perfect enough to render either generic or specific identification possible. The discovery of shale charged with the carbonized stems of plants below the Devonian limestone of Iowa is a matter of much interest. Frequent reports have gained circulation of the discovery of coal in drilling wells in regions occupied by Devonian rocks. From Jesup, Janesville, Marion, Davenport, and other places, such rumors have gone out. In one or two cases, shafts have been dug at considerable expense, necessarily ending in disappointment and failure. The discovery at Independence accounts for these reports. In drilling through the limestones, the lower shales, with their carbonized plants, were reached, and the dark color of the borings, mixed with fragments of real coal, naturally enough gave rise to the impression that a veritable coal-mine had been found. It is to be noticed that all the places from which such reports have come stand near the eastern outcrop of the Devonian, where its entire thickness could be pierced at a very moderate depth. The number and position of such localities would show that the shale in question is not a mere local deposit, but is distributed all along the outcrop of Devonian rocks in Iowa. The researches of Mr. Deering and myself have brought to light quite a number of finely preserved Brachiopods, representing fourteen species. Of these, two are not determined and five are new to science; but the chief interest attaches to certain species that have hitherto been known only from the shales of bed No. 3, near Rockford. It will be convenient to arrange the specimens in three groups as follows:— I. Species limited in Iowa, so far as known, to the Independence shales: Strophodonta variabilis, n. s.; Gypidula munda, n. s.; Orthis infera, n. s.; Rhynchonella ambigua, n. s.; Spirifera subumbona, Hall (?). II. Species ranging throughout the entire group, and so common to beds 1, 2, and 3: Atrypa reticularis, Linn. III. Species common to beds 1 and 3, but not known to occur in the intervening limestones: Strophodonta quadrata, n. s.; S. arcuata, Hall; S. canace, Hall & Whitfield; S. reversa, Hall; Atrypa hystrix, Hall;* and Productus (Productella) dissimilis, Hall. *The form designated here as A. hystrix, Hall, differs conspicuously from that described in Geology of Iowa, 1858, vol. i, part 2, p. 515, under the name of A. aspera var. occidentalis. This last occurs abundantly in the overlying limestones. The specimens from the lower shales are identical with the form presented by this Atrypa in the Rockford shales. For application of this specific name to this special form, see 23d Annual Report of Board of Regents on New York State Cabinet, p. 225. It is an interesting fact that of the twelve determinable species six occur only in the shaly deposits at the opening and close of the Devonian, notwithstanding these deposits are separated by 150 feet of limestone. Only one species is known to pass from the lower shales into the limestones above, and even there it appears under a form so altered that specimens from the two beds may be distinguished as readily as if they were distinct species. If we take form and surface-markings into account, the Atrypa reticularis of No. 1 also finds its nearest representative, not in the limestones immediately above, but in the shales at Rockford. Obviously, then, the Independence shales are more nearly related to the Rockford beds than to any other formation in Iowa. The species in Group I seem to have disappeared with the ushering-in of conditions under which limestones were formed; they maintained themselves in some locality which has not been discovered, or from which the shaly deposits have been entirely swept away, and returned with the return of conditions favorable to their existence during the deposition of the Rockford shales. The intimate relation between the two extremes of the group is certainly a most interesting one, and can but strengthen the conclusion of Dr. White, that all the Devonian strata of Iowa belong to a single epoch. Brachiopods of the Independence Shale. STROPHODONTA VARIABILIS, n. s. Shell small, very variable, thin, orbicular to semi-oval in outline. Valves in some instances about equally convex, in other cases, notably in young specimens, the dorsal valve has the greater convexity, the ventral being flat or even slightly concave; again the ventral valve may be regularly convex, the dorsal being concave, or the dorsal valve may be convex near the back, becoming deeply concave toward the front margin. Hinge line straight; cardinal extremities often produced, but more frequently rounded in adult individuals. Hinge-area common to both valves, narrow, a little wider on the ventral, marked by a few strong vertical striæ corresponding to the deep crenulations of the hinge-line. Surface marked by fine radiating and alternating striæ, which are strongly curved on the cardino-lateral areas and increase by implantation. Fascicles, of from 4 to 7 minute, low, rounded striæ, occur between each pair of larger, angular, and much more prominent ones. An imperfectly defined mesial fold sometimes seen on ventral valve. Stria crossed by very minute, microscopic, concentric lines. Muscular scars of ventral valve broad, short, and sharply defined by an elevated ridge. Cardinal process of dorsal valve bifid, the diverging parts slender, emarginate at tip, and fitting into notches in area of ventral valve. Entire inner surface granulose. Vascular markings obscure, except near the margin. Length, 12; width, 15; thickness, 4 millimeters.* STROPHODONTA QUADRATA, n. s. Shell small, concavo-convex, quadrate in outline. Cardinal extremities sometimes abruptly produced, sometimes rounded. Ventral valve very convex, flattened on the umbo, and descending abruptly to the lateral and front margins. Dorsal valve concave, following closely the curvature of the other. Hinge-area common to both valves, wider on ventral, finely striated. Foramen only sufficiently developed to receive the extremities of the bifid cardinal process. Muscular scars faintly impressed, not definitely bounded. Surface of ventral valve ornamented by fine radiating striæ. From 3 to 5 very small striæ are implanted between pairs of more prominent, but very slender, filiform, and often slightly interrupted ones. A broad, shallow, mesial sinus sometimes occupies the front half of the valve. On dorsal valve, the striæ are subequal, corresponding to the finer ones of the ventral. Length, 9; width, 11; convexity, 5 millimeters. STROPHODONTA ARCUATA, Hall. Strophodonta arcuata, Hall, Geology of Iowa, 1858, vol. i, part 2, p. 492, plate iii, fig. 1 a, b, c, and 2 a, b. Very common in the Rockford shales, and is also found at Independ ence. STROPHODONTA CANACE, Hall & Whitfield. Strophodonta canace, Hall & Whitfield, 23d Ann. Report on State Cab. of New York, p. 236, pl. xi, figs. 8-11. The specimens in hand present some differences from the Rockford forms. Other specimens from Independence show more exact agree ment. STROPHODONTA REVERSA, Hall. Strophodonta reversa, Hall, Geology of Iowa, 1858, vol. i, part 2, p. 494, pl. iii, fig. 4 a, d. From Independence. Also found at Rockford, where this species is very abundant. ORTHIS INFERA, n. s. Shell very small, orbicular or subelliptical; valves about equally convex. Ventral valve regularly convex, with a slight indication of a mesial fold; beak prominent, erect or slightly incurved; hinge-line short, length about equal to a third of the width of shell near the middle; hinge-area narrow. *All the dimensions given in this paper are taken from average-sized specimens, unless otherwise stated. |