The bedded trap and conglomerate are admirably exhibited on Keweenaw Point, and in many places in the Ontonagon district; but as we have minutely described the geographical distribution of all the trappean rocks of this era with the associated conglomerate and sandstone, in a former report, a further description is deemed unnecessary.

[The features of this sandstone are described as presented at various points north of the lake, at Presqu'Isle, Carp River, Grand Island,-where the variety of colors the rock presents has given rise to the name of "Pictured Rocks,❞—on the Menomonee River, White Rapids, etc.]

At the White Rapids, the sandstone is again exposed, presenting very nearly the same external characters, except that it is less discolored, and reposes on the uptilted edges of the quartz. It may be seen in some of the rapids below, and reappears, for the last time, in the river banks, forming ledges six or eight feet high, about three miles above the Big Bend, in township 35, range 29.

"* In this vicinity, Mr. Desor discovered, in some of the loose masses of this rock, other fossils than the Lingula, which are so characteristic of this group further to the east. These fossils consist of the fragments of one or more species of trilobites, resembling Asaphus. From the characters preserved in a single caudal extremity, one species is identical with that which occurs in the same rock on the Missisippi and St. Croix rivers.

From the Menomonee river, the Potsdam sandstone approaches within fifteen or twenty miles of the shore of Green Bay, being distinctly exposed on all the streams flowing into it. Continuing in the same direction, its easterly limit passes near the Great Bend in the Wolf river, northwest from the outlet of Lake Winnebago. From thence, meandering westerly, it follows nearly the course of Wolf river, crossing it in the neighborhood of Lake Pauwaiceen, and is thence prolonged southwesterly towards Green and Puckaway lakes. In the neighborhood of Pleasant Valley, about twelve miles west of Strong's Landing, on the Fox river, it is exposed in several low escarpments, succeeded by the calciferous sandstone, which here presents its usual characters. From this region, its southern limit stretches to the west and northwest. The country here presents a feature which continues to the Mississippi river. The hills appear to be outliers, capped by the calciferous sandstone or succeeding limestones, while the valleys and the lower part of the escarpments are composed of the Potsdam beds.

The description of the westerly prolongation of this sandstone is from the MS. of Mr. Hall.

The rock is fine grained, of a light yellow color and very friable. Some of the superior beds, which are thin, have been wrought for grindstones. The friable character of this sandstone is one of its most prominent features, and, owing to this circumstance, the escarpments are not usually high, or abrupt, unless it has been protected by the overlying rock. In its want of cohesion, it differs, in a very marked degree, from the prevailing character of this rock, as developed in New York and Canada, where it is usually, though not always, compact. It is not, however, unlike the sandstone of the Pictured Rocks, and is less friable than that of the Mississippi and St. Croix region.

The almost uninterrupted continuity with which this rock can be traced, even from its eastern extension through Canada and along the northern shore of Lake Huron to the St. Mary's river, and thence westerly, leaves no doubt as to its true position and identity in age with the Potsdam sandstone of New York. If we were at a loss in thus tracing it continuously, we have still the evidence of the succeeding fossiliferous strata, which show, conclusively, the same relations to this sandstone as they do to its equivalent in New York. With both these evidences combined, we cannot hesitate for a moment in our conclusion regarding its age and place in the series.

From the points just noticed, where this sandstone appears in eastern Wisconsin, it can be traced uninterruptedly across the entire breadth of the state to the Mississippi and St. Croix rivers. It is true, at the last named localities, we have the evidence of fossils which are not known to occur in its easterly extension; but we have already noticed the occurrence of the Trilobite on the Menomonee, while we have the Lingula everywhere, though in far greater profusion in the St. Croix region than elsewhere. In drawing inferences as to the age of the rock, from the occurrence of these fossils, it should be remembered that it is by no means improbable that similar ones may yet be found in more easterly localities. They seem to be coëxistent with calcareous bands, or the more calcareous portions of the group, and it is to this modification that we should look for the development of the fauna of this ancient period.

From all this evidence, we regard the question of the age of this rock as settled-that the Potsdam sandstone of New York is identical with that of the Mississippi and the St. Croix. One great source of doubt and perplexity in its determination, heretofore, was the recurrence of a sandstone identical in character with the lower, but superior in position to the calciferous sandstone, or lower magnesian limestone. It is a thin mass, evidently due to a recurrence of the same causes which produced the inferior deposit. This has been well elucidated by Dr. Owen in his reports on the upper Mississippi, in which he has shown that,

near the junction of the lower sandstone with the calciferous, there are several alternations of calcareous and silicious bands, the latter having the character of the sandstones below, and the former of the calcareous deposits above. These occur in several places on the upper Mississippi river, and give the geologist an introduction to that condition of things which subsequently produced the upper sandstone, which is distributed over a large part of Wisconsin, so often mistaken for the lower member of the series; but which, in fact, is separated from it by two or three hundred feet of calcareous rocks.

This upper sandstone can be regarded in no other light than as the result of the same causes which produced the Potsdam, and were suspended during the period of the deposition of the calciferous sandstone, or lower magnesian limestone, to be renewed, for a short period, in the deposition of a mass of sandstone, varying from fifty to eighty feet in thickness, upon the surface of the calcareous deposit. This fact shows the more intimate connection between these two lower groups than has heretofore been suspected. It is, nevertheless, shown in many places within the Lake Superior district, that the true sandstone, as it is traced upward, becomes gradually calcareous, and "finally passes into well-characterized, compact, magnesian limestone."* The same is true, also, of this rock, in Canada and New York; while, however, there is rarely any evidence of increase in the silicious materials towards the termination, as we observe in the west. In some localities, there are thin but distinct bands, near the upper portion, having an oolitic structure, which, as we go westward, appear to be replaced by beds of a granular texture and of a silicious character.

ART. III.—Analysis of Tin Pyrites; by Dr. J. W. MALLET.†

THIS rather rare mineral is one of which the chemical composition has appeared somewhat doubtful, owing to the considerable discrepancy between the three or four analyses which have been made of it, and to the fact that it almost invariably occurs massive and so intimately mixed with copper pyrites and other minerals as to render it difficult to select a fair specimen for examination. The locality from which most of the specimens in cabinets have been derived is Wheal Rock, near St. Agnes, Cornwall; but the mineral has also been observed in two or three other Cornish localities, and at Zinnwald, in Bohemia. I have recently received a specimen (name unknown) from a friend in England, which he states to have been found on St. Michael's Mount, + Communicated for this Journal.

* Part 1, p. 117.

SECOND SERIES, Vol. XVII, No. 49.- Jan. 1854.

5

Cornwall, and which, on examination, proves to be tin pyrites, and apparently in a purer state than any hitherto analyzed.

This specimen occurs in quartz which has obviously been taken from a vein in granite. The structure appears to be crystalline, although no distinct planes could be observed. The color is not steel-gray, as in that of the mineral from Wheal Rock, but iron-black, with slight superficial blue and red tarnish in some places. Streak black, lustre sub-metallic, fracture uneven. Hardness 4. Sp. gr. =4.522. Heated before the blowpipe, on charcoal, sulphurous acid is given off, oxyd of tin deposited in large quantity upon the charcoal, and a black globule obtained, from which copper and tin may be reduced on the addition of soda.

A carefully conducted quantitative analysis, in which chlorine was used to decompose the mineral, gave the following results.

Thus the relative number of atoms of sulphur, tin, copper, and iron and zinc, as given in the 2nd and 3rd columns above, are almost exactly as 8: 2:4: 2; whence we have the formula first assigned by Kudernatsch, (Pogg. Ann., xxxix, 146.) viz., 2(Fe S+ZnS), SnS2+2Cu2 S, SuS2. The present analysis agrees so closely with this formula, from which the results of Kudernatsch, and even those of Rammelsberg, (Handw. d. Chem. Theils d. Mineral. 2d Suppl., 179,) sensibly differ, that it seems fairly to be considered as representing the composition of the mineral in a pure state. The analysis also possesses some interest in showing the presence of zinc in considerable quantity, therein agreeing with Rammelsberg's analysis above referred to of the mineral from Zinnwald. It is to be observed that in both cases the iron and zinc occur in very nearly atomic proportions, so that perhaps the formula should be written 2FeS, SnS2+2ZnS, SnS2+2(2 Cu S, SnS2), though this does not seem very probable, since Kudernatsch found 12:44 p. ct. of iron to but 177 of zinc, while Johnston gives 10-113 p. c. of the latter to 4791 of the former, as contained in tin pyrites (from the same locality as the specimen submitted to the present analysis, St. Michael's Mount). The presence of this large quantity of zinc, is however of importance, chiefly as proving that the tin must enter into the composition of the mineral as bi-sulphuret, since the other formula which has been proposed, namely, 2SnS, FeS2 +2Cu S, FeS2, would

require us to admit the presence of ZnS2, whereas no such compound is yet known either occurring in nature or formed by artificial means. It is remarkable that Fahlerz, the only other compound sulphuret in which zinc occurs in notable quantity, is the mineral whose composition (4(RS), SbS3) seems to approach most nearly to that of tin pyrites, the latter containing two instead of four atoms of the sulphur bases to one of sulphur acid, and this electro-negative sulphuret being bi-sulphuret of tin, instead of ter-sulphuret of antimony. Indeed, some real connection between these two minerals seems to be further indicated by their occurrence in the same crystalline system, and their close resemblance to each other in hardness, specific gravity, and general physical characters.

ART. IV.-Notice of the Hail Storm which passed over New York City, on the first of July, 1853; by ELIAS LOOMIS, Professor of Mathematics and Natural Philosophy, in the University of the City of New York.

On the first of July, 1853, a very remarkable hail storm passed over the city of New York. The day had been uncommonly hot and sultry, the thermometer having risen to 90 degrees, and the air was believed to contain an unusual amount of vapor. A little before 5 o'clock in the afternoon, a heavy black cloud was observed to rise in the northwest, the wind at the time blowing moderately from the northeast, and subsequently from the east. As the cloud advanced and covered the northwestern sky, while it was still clear in the southeast, numerous streaks of zigzag lightning appeared to issue from the front margin of the cloud and descend towards the earth. I noticed the approach of the storm from my lodgings in Eighth street, within a quarter of a mile of the University. About five o'clock the wind came strong from the northwest, and the rain poured down in torrents. Presently I heard a loud thump upon the roof of the opposite house; soon another thump; and presently a third and fourth. I was not long in discovering that the noise was produced by the fall of hailstones of a size such as I had never before witnessed. They were few in number-but their average size was little less than that of a hen's egg; and one or two I am persuaded were fully as large as my fist. They almost invariably broke on striking the pavement; so that I could not secure either of those large stones except in fragments; and moreover the rain was falling in torrents. I however hastened to the yard in the rear of the house, hoping to find some upon the grass which had not been broken in the fall. After the rain had nearly subsided, we