1. Note on the supposed Fossil Footmarks in Kansas; by C. H. HITCHCOCK. (Communicated for this Journal.)-In this Journal, II, vol. xli, p. 174, is a description by Prof. B. F. Mudge of Kansas, of a slab containing four impressions referred to Leptodactylous birds. The rock was conjectured to belong to the Lias, and the specimen was obtained from the top of a bluff one hundred and twenty-five feet above the level of Republican river, in the central part of the State. The slab was much weathered, and careful search brought no other instance of the impressions to light.

It was my fortune to examine this specimen at Manhattan the past summer, but during the absence of Prof. Mudge. It had been suggested by eminent authority that these impressions were probably the marks of exogenous leaves. Little credence was given to this view, inasmuch as Prof. Mudge had favored us years before with a careful drawing of the slab; yet we were not prepared for the disappointment produced by the first glance at the slab. No two of the impressions were alike, and they had been obviously chipped out of the stone by the aborigines.

By reference to the description, it may be said that impression A is very much narrower than B, and less skillfully excavated. The edges are rough. Between C and D there is great dissimilarity. The middle toe of the first is very much longer than either of what might be called the middle toe of D, the latter having four toes. The divarication of the toes in A does not correspond with that in B, nor that of C with D, as ought to be the case if these footmarks had been made by the stepping of an animal.

The physical character of the impressions shows them to be unlike íchnites; for the excavation has a sharp edge, while the surface slopes gradually from the top of the layer to the bottom of the furrows in all genuine footmarks.

It is not the first time that aboriginal markings have been mistaken for animal remains. In the Hitchcock Ichnological Museum, Case No. 31, are numerous examples from Westmoreland county, Pennsylvania, of the same character. The roughness of the marks is more obvious than in the Kansas specimens, while the imitations of the tracks of dogs, birds, and other animals had received long generic and specific names. (See this Journal, II, vol. i, p. 268, 1846.) I have also heard of several cases not described in any scientific communication, but mentioned by friends. Hence, it appears to have been a habit of the aborigines to engrave upon the rocks imitations of the feet of animals, whether undesignedly or not does not appear.

The rock resembles some portions of the Connecticut River Sandstone, and it may be that genuine impressions will yet be discovered in Kansas. Prof. Mudge has manifested great enthusiasm in collecting specimens in the State of his adoption, and we anticipate the appearance of valuable papers from his pen.

In this connection it may be worthy of remembrance that in 1866 I found a single impression of the Cheirotherium on the Delaware river in Pennsylvania, a few miles below Easton, and that in the following year I found on the New Jersey side an impression of the Grallator gracilis, and one or two small reptilian ichnites. These are all Triassic.

26 Pine st., New York, Nov. 2d, 1868.

2. On Ivigtite; by G. HAGEMANN.-Over a year ago I made some examinations of a mineral occurring in the cryolite of Greenland; but as my analyses were too imperfect to determine therefrom a new mineral species, I did not publish them. Mr. Theo. D. Rand has, however, recently published a still more incomplete analysis (see this Journal, II, xlvi, November, 1868) of the same mineral, which he has named ivigtite, and I think it therefore proper also to make my examinations known, as they may throw some more light on this species.

Besides the occurrence already mentioned by Mr. Rand, ivigtite is found in small veins passing through the cryolite without reference to its cleavage. It has then a gold-yellow or pale-green color, and forms radiated plates, which seem as elastic as mica. I have also found it forming single stars of radiated plates in the solid cryolite. Sometimes the veins thicken, and the ivigtite appears then as an olive-green solid mass, often quite transparent.

It does not fuse before the blowpipe (Mr. Rand has probably got his sample mixed with cryolite, as he has found it to melt readily). It dissolves in borax with an iron and silica reaction. When heated in a closed tube it affords water with an acid reaction. Analyses I. and III. were made by fusion with carbonate of soda; II. was decomposed with fluohydric acid.

Adding the alkalies to analysis III, we have

Ši 42.82, Fe 13.06, Al 27·03, Ña 10-27, È 1·05, H 3·93, F tr. = 98·16. This would give nearly the ratio of a unisilicate, 1:6: 8: 1, and the formula:

3(Al,, Fe,)Si2+ (Ña, K)ŝi + HO.

The great difference between Mr. Rand's and my analyses can perhaps be accounted for by Mr. Rand's having had a considerable quantity of cryolite in his sample. The cryolite would increase

the soda and decrease the alumina and silica. This would perhaps account also by its fluorine for a loss of 11.68 per cent in Mr. Rand's analysis. Of my samples, I. was not entirely free from cryolite; II. was more so, and III. I should judge almost entirely.

3. Notes on the Chemical Geology of the Goldfields of Califor nia; by J. ARTHUR PHILLIPS. Communicated by Prof. A. C. RAMSAY. (Proceedings Royal Soc., xvi, 294.) (Abstract.)

Rocks of the Gold-Regions of California.-The great sedimentary metallic belt of California lies on the western slope of the Sierra Nevada, beginning in the neighborhood of Tejou Pass, and extending through the state to its northern limit. In consequence, however, of various local circumstances, different portions of this band are of very unequal importance as gold-producing districts.

The slates of the auriferous belt have been shown by Professor Whitney to belong, for a great extent, to the Jurassic period, although the occurrence of numerous Triassic fossils in the goldbearing rocks of Plumas county and elsewhere renders it more than probable that no inconsiderable portion of the slates in the heart of the gold region are of that age.

The rock constituting the principal mass of the Sierra Nevada is a granite containing only a small proportion of quartz, and in which but one species of feldspar (oligoclase) is generally found.

Lying between the band of metamorphic slates and the great central mass of granite forming the more elevated portions of the chain, are found various crystalline rocks, such as syenites, diorites, and porphyries.

Quartz Veins.-The matrix or gangue of the auriferous veins of California is invariably quartz, which is generally crystalline in its structure, or partially vitreous and semi-transparent. In the majority of cases the quartz constituting an auriferous veinstone is ribboned in such a way as to form a succession of layers parallel with the walls of the lode itself; and some one or more of these laminæ are not unfrequently far more productive than all the others. In some instances these parallel bands are separated from each other by a thin layer of quartz, slightly differing, either in color or structure, from that forming the seams themselves; or they may be only distinguished by a difference of color of two adjoining members of the series.

In many cases, however, laminae of the enclosing slates divide the vein into distinct bands; and in such instances it will be observed that the thickness of the interposed fragments of slate is sometimes not greater than that of a sheet of the thinnest paper. Cavities or druses containing crystals of quartz occur in all the auriferous veins of the country; and a certain amount of crystallization may also not unfrequently be remarked along the lines of junction of the several bands of which a vein is composed. In addition to ordinary quartz, in a more or less crystalline form, amorphous hydrated silica, or semiopal, and chalcedony are occa

sionally met with; in some instances the opal is interfoliated between layers of true quartz, and is sufficiently auriferous to repay the expenses of treatment.

The metallic minerals enclosed in the gangue of auriferous veins are ordinary iron pyrites, blende, and galena, and less frequently, arsenical pyrites, magnetic and copper pyrites, and cinnabar. These sulphids invariably contain gold; and veins in which some one or more of them does not occur in considerable amounts, are not regularly and lastingly productive.

Near the surface the iron pyrites and other sulphids become decomposed by the action of air and the percolation of meteoric water through the mass, staining the quartz of a red or brown color, and leaving the gold in a free state. Under such circumstances numerous cubical moulds of iron pyrites are found in the veinstone; and although this mineral has been entirely removed by chemical action, the cavities left contain finely divided gold, obviously liberated by the decomposition of pyrites.

Beneath the line of natural drainage of the country the sulphids remain undecomposed; but if rock containing pyrites be placed in nitric acid the sulphid becomes dissolved, and finely divided, crystalline, or filiform gold will partially occupy the resulting

cavities.

In one of the detrital beds in the vicinity of the village of Volcano in the county of Amador, and elsewhere, distinctly marked quartz veins may be observed cutting through the gravel, and evidently formed by the action of water holding silica in solution.

Attention has also been recently directed to bands of auriferous slate found in the copper-bearing belt west of the main gold-belt of the State, and in the foot hills of the Sierra. In this locality the gold, instead of being obtained from a well defined vein, chiefly composed of ordinary quartz, is inclosed in a band of siliceous slaty rock, extending northwest and southeast, and dipping in conformity with the other strata of the district.

The number of fluid-cavities contained in the veinstones of the auriferous lodes of California is seen under the microscope to be exceedingly limited; and in order to obtain sections affording good examples, even of small size, it is necessary to select such bands as may be more than ordinarily crystalline, or to operate on thin fragments of crystals sometimes found lining the interior of drusy cavities. In the more opaque and generally most auriferous portions of veins, the cavities are numerous but exceedingly small, and are often so opaque, apparently rendered so by being internally coated with a lining of clay, that no vacuities can be distinguished.

Out of more than fifty sections of veinstone examined, only some six or seven were found to contain fluid-cavities of sufficient size to admit of any attempt at accurate measurement by means of ordinary appliances; but in all cases there appeared to be considerable differences in the relative dimensions of the vacuities and

the enclosing cavities, and the temperatures at which they severally became filled were consequently ascertained by direct experiment. In every instance they were found to require very different degrees of heat to become full, since in the same specimens some of the vacuities disappeared at 180° Fahr., others filled at temperatures slightly above that of boiling water, whilst many, though much reduced in size, remained perfectly visible at 365° Fahr.

Alluvial Deposits.-Although a very large amount of the gold annually obtained was no doubt originally derived from auriferous veins, not more than about one-third of the precious metal collected is procured directly from that source. The larger proportion of the gold now brought into the market is derived from alluvial diggings, in which it is separated by washing from the clay, sand, and gravel with which it is associated.

This gold-bearing drift belongs to at least two distinct geological epochs, both comparatively modern-although the latter period is distinctly separated from the earlier, its materials being chiefly derived from the disintegration and redistribution of the older deposits.

În California the more ancient deposits or "deep placers referable to a river-system different from that which now exists, flowing at a higher level, and frequently nearly at right angles to the direction of the main valleys of the present period.

The deep placers are in many localities covered by a thick capping of lava; and the eruptive matter covering them often occurs in the form of basaltic columns, beneath which are found the layers of sand, gravel, and boulders with which the gold is associated. The wood which occurs in these gravel-beds is either beautifully silicified, or is replaced by iron pyrites.

In the more clayey strata of these deposits leaf beds and impressions of leaves are not unfrequently found; and an examination of these made by Dr. Newberry authorizes the conclusion that the auriferous deposits lying beneath the lava are of tertiary age, and that they probably belong to the later Pliocene epoch. Waterworn gold is disseminated throughout the whole mass of these deposits, not, however, with uniformity, but always in greater abundance near the bottom, and more particularly in direct contact with the "bed rock," which is invariably grooved and worn by the action of water.

The materials of which these deep placers are composed are frequently consolidated into a sort of hard concrete, by being firmly bound together by crystalline iron pyrites; and sometimes this cementing material consists either of carbonate of lime or silica. The silica is rarely met with in a crystalline form; but near Kenebeck Hill a cavity, resulting from the junction of several pebbles, was found completely lined with well-defined crystals of quartz These did not show, under the microscope, the usual fluid-cavities of quartz of the ordinary quartz veins of the country.

Where the cementing material of the conglomerate chiefly consists of pyrites, the enclosed trunks of trees are usually replaced