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 Airypa 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.*
Known only from the Independence shales.

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.
Occurs both at Independence and Rockford.

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, 11. 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.

Dorsal valve convex, with a fairly defined mesial sinus that is wide in front and narrows rapidly toward the beak; beak only a little less prominent than on ventral valve. Surface of both valves marked by from 24 to 30 moderately strong, rounded striæ that are separated by wide furrows and multiply by bifurcation on the front half of shell. Striæ and furrows crossed by very minute microscopic lines.

Length, 6; width, 7; thickness, 3 millimeters.

Known at present only from the dark shales at Independence.

ORTHIS, sp.?

The surface is marked by coarse, angular striæ, and a sharp angular mesial ridge gives the valve a carinated appearance. From the Inde. pendence shale.

SPIRIFERA SUBUMBONA, Hall.

Spirifera subumbona, Hall, Pal. N. Y. vol. iv, p. 234, pl. 32, figs. 22-30.

The specimens under consideration agree very well in most characters with some forms of Spirifera subumbona, but, as will be seen from the figures, they differ materially in size and in the width of the hinge-area. Not known to occur in Iowa except in the Independence shales.

ATRYPA HYSTRIX, Hall.

Atrypa hystrix, Hall, Pal. N. Y. vol. iv, p. 236, pl. 53, A, figs. 15-17. A. hystrix, H. & W., 23d Annual Rept. N. Y. State Cabinet, p. 225. (See note at bottom of p. 726 of this Bulletin.)

The specimen in hand was collected at Independence.

ATRYPA RETICULARIS, Linn.

Atrypa reticularis of authors.

The specimens collected represent the prevailing type as this species. occurs in the lower shale at Independence. It is more nearly related to Rockford forms than to the forms found in the limestones only a few feet above.

RHYNCHONELLA AMBIGUA, n. s.

Shell large, transversely oval or elliptical; valves moderately gibbous, subequally convex; mesial fold and sinus broad and well developed at the anterior margin in full-grown shells, becoming obsolete toward the umbonal region. Length and width in about the ratio of 3 to 4. Ventral valve regularly arched in the posterior part; the middle of the anterior half of the valve occupied by a broad sinus, which becomes deep and subangularly margined toward the front. A strong fold, extending about a third of the way to the beak, occupies the middle of the sinus; rudimentary folds appear on either side of the middle in the sinus of large shells. Beak of ventral valve projecting slightly beyond the other, closely incurved and appressed so as to show neither area nor

foramen in perfect adult shells. Dorsal valve convex; greatest convexity near the umbo, from which it slopes gradually to the lateral and anterolateral margins. Mesial fold confined to anterior half, broad and high in front, and divided in the middle by a wide, longitudinal, subangular furrow; rudimentary furrows on either side of the middle. Both valves with three or four plications on either side of mesial fold and sinus in adult shells; plications confined to antero-lateral margins.

lateral margins and umbonal region smooth. Shell thin, translucent, scarcely fibrous.

. Dimensions of a large specimen are: Length, 28; width, 41; thickness, 23 millimeters.

Confined, as far as known, to the dark shales at Independence.

GYPIDULA MUNDA, n. s.

Shell small, subtriangular to broadly ovate, inequivalve; ventral valve convex, curving almost regularly from beak to front margin; beak only moderately prominent, obtuse, slightly incurved; an indistinct mesial fold near the front margin. Dorsal valve transverse elliptical in outline, slightly convex near the beak, sloping at first somewhat abruptly and then more gradually toward the cardino lateral margins; a broad sinus, of which the middle is occupied by a single low fold, is confined to the anterior margin. A few indistinct folds occupy the antero-lateral margins of both valves; surface otherwise smooth.

Area and foramen as in other species of this genus.
Length, 8; width, 10; thickness, 6 millimeters.

This species resembles Gypidula occidentalis, Hall, from which it may be distinguished by its smaller size, less prominent beak, greater proportionate width, and deeper sinus. The young G. occidentalis of corre sponding size are entirely smooth, and show no trace of either fold or sinus. They differ also from G. munda in form and general proportions. From the dark shale at Independence. The species is unknown from any other horizon.

PRODUCTUS (PRODUCTELLA) DISSIMILIS, Hall.

Productus dissimilis, Hall, Geology of Iowa, 1858, vol. i, part 2, p. 497, plate iii, fig. 7 a-c.

This species is abundant at Rockford, and is among the most common species in the Independence shales.

PRODUCTUS (PRODUCTELLA) sp.?

The collections from the Lower Devonian Shales contain a few specimens of this small Productus. It is somewhat related to P. Shumardianus, Hall. More material will be necessary before it can be determined.

ART. XXXI.-ON THE MINERALOGY OF NEVADA.

BY W. J. HOFFMAN, M. D.

This report is based primarily upon the collection made in 1871 while a member of the expedition for the exploration of Nevada and Arizona.* Since that time I have received well-authenticated species from various sources, chiefly in Nevada; and those which have not come under my personal observation have been accredited to the proper authorities. The original collection is now at the National Museum, excepting in a few instances, in which the materials were consumed in making the necessary analyses. The only interesting feature which I shall mention. here is the occurrence of manganiferoas compounds in a belt of limestone, chiefly traceable from Austin south, and eastward toward Hot Spring Cañon. Most of the compounds containing antimony in various forms occur chiefly throughout the western portion of the State, while in the eastern portion the haloid compounds predominate. Neither of these, however, are in any way governed by the occurrence of so-called "sulphuret ores", as these are distributed pretty generally.

In addition to the above, a few remarks upon, and a list of, the thermal and mineral springs visited are added; also notice of some of the rarer minerals found in Owens Valley, California.

I embrace this opportunity of acknowledging my indebtedness to the following-named gentlemen for information and specimens which I could not have obtained through any other sources: Mr. Julius Partz, superintendent and afterward assayer of the mines in Blind Springs District, California; Mr. Richard Stretch, formerly engineer of the Virginia City Mines; Mr. Leon and the Canfield Bros., Belmont; the Messrs. Ogden, of Morey; Thomas Shaw, Gold Mountain; and Mr. W. S. Keys, superintendent of the Eureka Consolidated Mines. Dr. A. E. Foote, of Philadelphia, Pa., furnished me with several names, to which (when not on my list) his name has been appended as authority. In several instances, also, I have quoted from Professor Dana's Manual of Mineralogy for localities unknown to me personally. The localities cited are those in which the specimens named occur or did occur in their greatest purity or finest crystallizations.

Agate. See Silica.

Albite. In rhyolite, at Eureka and at Morey; massive, granular, at various points in Fish Lake Valley, rarely in crystals. Fine crystals in trachyte on the Colorado River.

* Now known as United States Geographical Surveys West of 100th Meridian.