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new class of fossils to the Troy fauna, and gives us, moreover, another example of a fossil species having an extensive geographical range.

It occurs in the coarse red-and-yellow-weathering slates of the Lower Potsdam group at Troy.

During the past season I paid a large number of visits to the first band of limestone met with in going eastward from Troy, and which, in a former paper, I have characterized as limestone band No. 1. (This Journal, Aug., 1873) As the result of this I succeeded in obtaining several species of fossils not previously known from this band, although known to occur in the other limestone beds of the Troy Primordial, and along with these a single head of a new and very pretty Trilobite of the genus Microdiscus. This I shall describe for the present as follows: Head, broadly rounded in front, nearly semi-oval in outline, greatest width at about the mid-length, slightly narrowed in passing backward from this point to the angles. Glabella conical, about two-thirds the length of the head, with two straight, moderately deep furrows extending all across, dividing the glabella in advance of the neck-furrow, into three parts of nearly equal length. Neck-furrow extending all across and deeper than the other glabellar furrows. The form of the neck segment cannot be clearly made out owing to the damaged condition of the specimen at this point. Dorsal furrows narrow, not deep, dying out toward the front of the glabella. Cheeks prominent, much swollen in the posterior third, without eyes or sutures. Marginal rim well defined all around, widest in front, with a conspicuously raised edge, inside of which there is a nearly flat or feebly concave space, and so bent upward in front as to give to the head on a side view a kind of slipper-like appearance On either side of the head, just inside of the raised marginal edge, there are three small tubercles situated within the limits formed by a line drawn across the head through the middle of the cheeks and another drawn parallel with it just in advance of the front of the glabella.

Greatest width of the head 14 lines; length along the median line, including the neck-segment, the same. Differs from Microdiscus (Agnostus) lobatus Hall (Pal. N. Y., vol. i, p. 258, pl. lxvii, figs. 5 a-f), from the same locality, in its shorter and transversely furrowed glabella, its tuberculated margin, and in its general proportions.

For this species I propose the name Microdiscus Meeki, in honor of Mr. F. B. Meek, whose labors in the cause of science have so vastly contributed to advance our knowledge of American Paleontology.

Occurs in conglomerate limestone of the Lower Potsdam group at Troy.

Troy, N. Y., Jan. 15, 1876.

ART. XLVI.-On a simple and very accurate method of tuning two Forks to unison; by ROBERT SPICE, F.C.S.

THOUGH the optical method of tuning, of Lissajous, gives good results, I find that two forks thus tuned to unison, may be a fraction of a vibration out, without in any way disturbing the steadiness of the figure.

In the 2d edition (English) of Tyndall's "Sound," in lecture VII, the author says, "I divide this jar by a vertical diaphragm, and bring one of the forks over one of its halves, and the other fork over the other. The two semi-cylinders of air produce beats by their interference. On removing the diaphragm, the beats continue as loud as before, one half of the same column of air interfering with the other."

Dr. Tyndall does not, however, mention the fact, that precisely the same result would have been obtained if no diaphragm had been employed, yet this is so. When two unison forks are struck on the knee, (or by a piece of lead covered with leather,) and then held together over their proper resonant column, the following phenomena will be observed.

If there is a difference between their rates, of several vibrations, there will of course be rapid beats; if the forks are very nearly in tune, the beats will succeed each other at long intervals; further, when they are almost perfectly in tune, there will not be any beats properly so called, but after the sound of the forks has nearly died away, it will rise or swell out again very slightly, proving that there had been interference.

Finally, when the forks are absolutely alike, there will be a gradual decrease of sound, down to silence, without any reinforcement at any time.

I find that to carry out this tuning absolutely, both forks must be at the same temperature; consequently, after using a file on one of them, I place both forks in a vessel of water to equalize their temperatures, wipe them dry, and test them. To show the accuracy of this method I select the following example:

A pair of Ut forks (256 vibrations) will sound over a column for about 135 seconds; suppose that the sound decreases up to the 100th second, and then begins to rise; obviously 100 seconds is the time of half a beat, or 200 seconds the beating time; that is to say, it will have been demonstrated that one of the forks gave of a vibration per second more than its fellow.

What has been said of the unison, applies to other intervals. I have recently executed by this method, Ut,, Ut,, Ut, and Ut, forks for the physical cabinet of Columbia College. 230 Bridge Street, Brooklyn, Jan., 1876.

ART. XLVII.—Silica of grasses and other plants carried up as Di atoms or other siliceous grains, and not in solution or as soluble silicates: by Prof. P. B. WILSON.

My attention was called, some time since, in the examination of the ash of plants obtained by slow incineration in a platinum crucible, to the fact that when the ash is treated with dilute acid, and evaporated to dryness on the water bath, it does not pass into the gelatinous condition prior to complete decomposition of the hydrated mass, as is the case with the silicates soluble in acid, or those decomposed with sodium and potassium carbonates. If, however, the ash, prior to the treatment with acid, is subjected to a high temperature, a combination of silicic acid with the alkalies, the alkaline earths, and the earths takes place, if all are present; then the silica separates in the gelatinous form and presents all of the chemical reactions of silicic acid obtained from the natural silicates. The silica obtained from ash by either of the processes indicated, on close examination, was observed to be entirely free from any combination, showing that it had been assimilated in the free state.

To demonstrate this theory, my friend G. I. Popplein, Esq., of this city, suggested the application of infusorial earth of the Richmond formation-found in large quantities on the western shore of the Chesapeake bay-to land sown in wheat. I have obtained straw from wheat so grown, and have found, after it has been treated with nitric acid, and the siliceous remains placed on the field of the microscope, that it consisted wholly of the siliceous shields of Diatomaceæ, the same as found in the infusorial earth, excepting that the larger discs in their perfect form were absent (Actinocyclus Ehrenbergii and Actinoptychus undulatus). My conclusions are that they, and there probably may be other forms, are too large to enter the root capillaries. During the coming summer I will attempt if possible to make micrometer measurements of both.

The discovery of Diatomacea in their original form in this wheat straw precludes the possibility of the infusorial earth having undergone any chemical change in the soil, either by forming chemical combination with the alkalies, or the earths, or by suffering physical disintegration from any catalytic action of any salts present in the soil

On

In the particles of silica placed upon the glass slide, when they were completely separated from each other, the outlines of the individual diatoms were sharply and distinctly defined. the other hand, when the physical action of ebullition with nitric acid was not sufficient for the complete separation of the AM. JOUR. SCI., THIRD SERIES-VOL. XI, No. 65.—May, 1876.

particles of the epidermal shield, there was observed a marvelous interlacing of the various forms, showing that they were conveyed by the sap cells directly to the section of the plant where they were destined to complete its structure. I have examined several specimens of straw, taken at random in the market; the silica in each specimen consisted of plates, very thin, and truncated at the corners.

The result of these investigations shows the necessity of finely divided silica in the soil, so minute as to be capable of passing with facility through the sap cells; secondly, that simple or compound silicates are useless as fertilizing agents, either natural, or artificially prepared. We have no valid reason for forming any theory that vegetation can, through any known chemical law, separate the elements or their compounds from combinations so positive in their character.

In this case we have a practical result capable of being verified at any stage of growth of a plant, produced by the application of silica to the soil in the form of certain well defined microscopic organisms; for, finding these in the ash to the exclusion of other particles of silica, they seem to be more acceptable for the plant structure. Free silica is hence the only condition in which it can enter the plant.

I look upon this discovery as leading agricultural investigations in a new direction, and it must eventually change many of the views expressed and accepted by scientists.

Every precaution was used in having all the material thoroughly cleansed, with a view both for accuracy and for removing suspicions that these microscopic forms were the result of dust showers.

Washington University, Medical department, Baltimore, Md., February, 1876.

ART. XLVIII.-The Conglomerate Series of West Virginia; by WILLIAM M. FONTAINE.

[Concluded from page 284.]

DR. STEVENSON, in his "Notes on the Geology of West Virginia," (read before the Am. Phil. Soc., Feb. 5, 1875,) speaks as follows of the "Great Conglomerate" of Randolph county. "This rock forms the crest of Rich Mountain for nearly sixteen miles within the region examined. For the most part it is a coarse sandstone, loaded with pebbles from one third of an inch to two inches in diameter. Along the Staunton Pike it shows some layers of slightly micaceous and very compact sandstone near the bottom. Here it is greatly increased in thickness; near the northern line of the state it is barely 350 feet thick, but in Randolph county it is not less than 600." He further says, "On the

Staunton Pike, along the east slope of the mountain, there was seen midway in the conglomerate, what appeared to be the blossom of a coal bed. As I had observed no evidences of coal in the conglomerate northward from this locality, this exposure was studied with some care, but nothing definite could be ascertained. Six miles farther south, on the same side of the mountain, a small coal bed occupies this place on the property of Mr. Bradley. There it is three feet thick." Dr. Stevenson also points out the mistake made both by himself, and myself, in admitting the presence of coal in the conglomerate of Monongahela county.

Dr. Newberry has shown that the Sharon coals of Pennsylvania, which are in the reports of the first survey put under the conglomerate, are really of later age. There remains then no case where coals are found within the rock in its extension northward. As is well known, the conglomerate in Pennsylvania north of this part of West Virginia, has thinned down to a homogeneous rock of 100 feet and less. We must then look for the north extremity of the special basin in which the expansion of this rock took place, somewhere in Randolph county. In farther confirmation of this, Dr. Stevenson mentions the curious fact that in that county the upper Umbral shales, at one point, thin out entirely, and the conglomerate is in contact with the

limestone.

In Ohio, the reports of that State show that the conglomerate has become too thin to form a continuous stratum.

Proceeding southwest, from Ohio into Kentucky, we find the conglomerate series forming the west outcrop of the east Kentucky coal field, being the sub-conglomerate coals of that State. Mr. Joseph Lesley, (Proc. Am. Phil. Soc., No. 91,) in his account of this outcrop belt, shows that in that quarter the Umbral shales are entirely wanting, and that the coals under the conglomerate lie immediately on the sub-carboniferous limestone. He traces this outcrop from Carter county southwest to Clinton county, on the south border of the State. The thickening of the series in that direction shows plainly that his line of investigation diverged from the edge of the basin and approached nearer and nearer toward the central portions. He states that the series consists of two members, the upper one a conglomeratic sandstone, and the lower one a coal-bearing portion. The upper member thins in proceeding southwest, while the lower

*If Professor Tyson's section of the Cumberland basin be correct, then it is clear that northeast of Randolph Co., in Maryland, the conglomerate again has coal in its central portion. He gives on Savage River, above the Umbral shales, and including the so-called "Coal-Measure Conglomerate," a thickness of 451 feet In this space he places three coal beds, two feet, two feet six inches, and two feet thick. The entire mass is begun and ended with massive sandstones, having a similar structure to the New River field.

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