is, from top to bottom, soft, yellow, siliceous or sandy shale, with heavy interstratified layers of hornstone.

The rock is generally thinly dotted with siliceous-sometimes calcareous-concretions; the larger occurring in the upper, more calcareous portion, are often fine geodes of quartz lined with crystals; one locality, at least, affords rhombohedral forms.

An interesting feature of these rocks-in fact of the groupis the presence of Crinoidal limestone. It occurs at various elevations in intercalated beds, ranging from one to ten feet in thickness; some of these are pure grayish-white limestone made up of the crinoidal remains; others are impure and enclose silicified fossils. As might be anticipated, the Crinoids are the most abundant fossils. The silicified ones are found occasionally in place, but usually detached, on the hill-sides with the flinty frag ments, and in the soil; silicified Trochites of a large size, both circular and oval,-common also to the succeeding member,are found in many places.

Large Spirifers and Producti occasionally occur, but excepting perhaps Crinoids, fossils are not abundant, the conditions under which the rocks were deposited not having been favorably to animal life.

As we approach the topmost strata, the rocks, without affording any well marked limit, gradually run into

20. (b.) Cherty limestone.-This member though related to the last, differs in being a true limestone, in affording a brick-red soil, in the character of its imbedded masses, and in being much more fossiliferous. The fundamental rock is thick-bedded and impure, of a light blue color; it occurs occasionally in purer beds without flints, but, in the main abounds in reniform nodules of chert and in siliceous layers. The latter, which, by the way, are very characteristic, liberated by the removal of the calcareous matter that contained them, occur very generally on the surface and in the red soil, in rough friable masses having a porous sandy struc ture and a light yellow or gray color; they abound in species of the beautiful Fenestella, and often in a large undescribed (?) Orthis, as well as in other species.

The strata are sufficiently argillaceous to give the soil a clayey

consistence.

E

A most important economical feature of these rocks is the presence, especially westward, of iron ore which sometimes passes down into the member below. The soil everywhere contains sufficient oxyd of iron to color it deeply.

This member is mostly the surface-rock of the table-lands surrounding the basin, and usually appears a few miles in the rear of the escarpments, increasing in thickness as we approach the mountains on the east, or the hilly ridges of Southern Kentucky on the north and northwest. (§ 6.)

From my own observations, and the best data I can collect, I infer the member to be from 250 to 300 feet thick, making the entire group 450 or 500 feet.

Owing to the present imperfect state of our knowledge of American carboniferous species, it is impossible to give a satisfactory list. The following is presented.

ART. XXXVII.-On the Houghite of Prof. Shepard; by S. W. JOHNSON, of the Yale Analytical Laboratory.

Read before the Am. Assoc. for the Advancement of Science, at Albany, Aug. 1851.

ON

On page 314 of the Proceedings of the meeting of this Association held at New Haven last year, occurs a notice of the mineral Houghite by Prof. Shepard. More than two years since I noticed specimens of this mineral from Dr. Hough, and then purposed to examine it. The specimens which were in my possession at the time of the publication of Prof. Shepard's paper, and which furnished the material for my analyses, agree in the main. with his description; and it appeared improbable that any chemical species could be made from them as they were exceedingly variable in composition as well as in appearance. It commonly occurs as small imbedded nodules, usually more or less flattened, with the interior dark gray or bluish gray and the exterior white. Experiment and observation unite in proving that the difference in color between the external and internal portions of these "concretions" is due to difference of composition. The milkwhite parts contain carbonic acid, the bluish-white portions do not. Further, some specimens are milk-white throughout, while others are almost entirely of a bluish tinge, and semitransparent. The specimens at my command for analysis were uniform in ap

pearance, but were more or less opake white externally and without exception were pervaded by minute grains of spinel and phlogopite. Some of them presented a portion just within the opake layer, that was transparent and homogeneous: within this, fragments and crystals of spinel predominated. These statements are necessary as a preface to the account of my chemical inves tigations, after detailing which, the physical properties will be again referred to.

The mineral subjected to analysis, comprised fragments partially opake and partially translucent, as it was almost impossible to procure by separation a homogeneous material. After ignition, it manifests an alkaline reaction, and this, as I have since found, it also does before heating.

As stated by Prof. Shepard, it is decomposable in acids, before and after ignition. A large nodule, slowly dissolves, even in cold acetic acid. Carbonic acid is evolved during solution, and in sufficient quantity to produce a precipitate on passing through baryta water. A residue has always occurred in my experiments, consisting in part of insoluble minerals,-spinel and phlogopite, and also in most cases of silica; and in fact, the mineral has often afforded a well characterized jelly with acids. The acid solution gives with ammonia, in presence of chlorid of ammonium, a copious white precipitate. The filtrate contains only magnesia, or occasionally a trace of potash, possibly from decomposition of phlogopite. The ammonia precipitate, as noticed by Prof. Shepard, yields alumina and a trace of iron to caustic potash, but is not entirely decomposed even by a large excess of it, during protracted digestion at a boiling heat. Following the usual routine of analysis it was repeatedly, and most carefully examined for all the salts and rare earths that can occur in such circumstances, but no evidence of their existence was obtained. It appeared to be a hydrous compound of magnesia and alumina, and upon reference to Gmelin's Handbuch, notice of such a substance was found. By three or four repeated solutions in hydrochloric acid, and precipitations by ammonia, it was completely separated into the two earths, alumina and magnesia; which with water completed the sum of its ingredients.

Previous to entering on the quantitative investigation of this mineral, I made inquiries of Dr. Hough, who resides near the locality, hoping to obtain homogeneous specimens. He could not furnish them, and the following analyses were made without expectation of perfectly accordant results.

In the analysis, carbonic acid was determined, in the usual manner, in a flask furnished with chlorid of calcium and aspirating tubes. Water was expelled by ignition, and collected in chlorid of calcium. The mineral was decomposed in hot hydrochloric acid, the whole evaporated to dryness, redissolved, and filtered;

in the solution, alumina and magnesia were separated by bicarbonate of soda; the magnesia weighed as pyrophosphate, the alumina, as such, after solution and reprecipitation by carbonate of ammonia. The insoluble residue was treated with hot solution of carbonate of soda, to extract silica.

Before subjecting the mineral to analysis, a portion in small fragments, the most homogeneous that could be selected, was used for determining its specific gravity. For this purpose after its weight had been taken, it was boiled in the water in which it was subsequently weighed, as air bubbles adhered to it very pertinaciously. The number 2.175 was obtained; but the mineral was afterward found to contain spinel.

A quantity of the mineral after being pulverized, was placed in a Liebig's drying tube, and exposed in a current of dry air to a heat of 100° C.; it lost water for a long time. The heat was afterward raised to 175° C., and it continued to lose weight for several days. It was finally submitted to the highest temperature admissible in an oil-bath, 280° C. (536° F.), and after more than 100 hours of drying, it ceased to lose weight. As this result had not been foreseen, the original weight of the mineral was not taken; the loss was at least five per cent.

A fresh portion of the mineral including that employed in taking the specific gravity, was carefully intermingled, pulverized and dried over SO3 in vacuo.

Two determinations of carbonic acid gave respectively 6.712 and 8.094 per cent.; mean, 7-380 per cent. Another portion, the only remaining material, was ignited until it ceased to lose weight. It then contained no carbonic acid. The loss was 40-857 pr. ct.

It was analyzed with the following results.

ΑΙ

30-048

Mg

55 467 insol. (spinel and mica) 15-196, Silica, trace =100′′711 Several water estimations were made, varying from 33 to 41 per cent., but I attach no value to them. If we subtract 7.380 the mean result for carbonic acid from 40-857 the total loss on ignition, we obtain 33-477 as the per-centage of water; rejecting the insoluble minerals and calculating the remaining constituents on 100, the composition stands as follows:

Excluding, in both analyses, all the ingredients but alumina and magnesia, and reducing these to per-centage relations, we find the following numbers.

These accordant results indicate the existence of definite relations between these two ingredients. Divison by the equivalents, gives the ratio of 4 of alumina to 19 magnesia, corresponding to alumina 35 15, magnesia 64.85. The ratio of 1: 5 would require alumina 33-53, magnesia 66.47.

It seems useless to speculate on the constitution of Houghite without new analyses.

Quite recently, I have visited the locality in company with Dr. Hough. It is in the town of Rossie, and near the village of Somerville, in St. Lawrence county, N. Y. The mineral occurs disseminated through white crystalline limestone, at the summit of a slight elevation, near which occurs beds of the Potsdam sandstone. Associated with Houghite are dolomite of variable composition, scapolite of brown and green color, phlogopite, graphite, spinel, and a crystallized pseudomorphous (?) yellow serpentine, in which I have obtained the water and silica percentages of that mineral.

Much of the rock exhibits evidences of atmospheric action. The serpentine in the altered parts has become discolored and so friable as to yield to the pressure of the fingers. The nodules of Houghite are half exposed, easily detached from the rock, and often opake and milk-white throughout.

This altered or bleached appearance in the rock does not occur upon the uppermost surface, as far as I have observed, but along its sides and under portions pendant over a cavity. But not a nodule of Houghite has been found even in the least altered rock that has not presented superficially in some parts a milkwhite color.

Among the masses which furnished material for analyses, I found several specimens that exhibited unequivocal evidences of octahedral crystallization, one of which is

here represented. Some of them are ths of an inch in diameter; they are superficially grooved and contorted, their edges are rounded, and protrude beyond the planes of the faces. In some an appearance occurs, which seems as if it had been produced by a protrusion, near the edge of each plane, leaving a line of depression with reëntering surfaces, corresponding to the lateral edges of a perfect octahedron,

while on the faces, a triangular depression occurs, bounded by the protruded edges of each plane of the crystal. In one nodule there is a gradual transition from the soft and amorphous Houghite, to the hard and regularly terminated spinel. The crystals are occasionally compound.