employed in experiment No. 8. This gave a feeble current and the carbon was rapidly polarized.

Ex. No. 13. As solutions of sulphurous acid and acid sulphites dissolve zinc without evolution of hydrogen, forming hyposulphites, it was thought that these might be used as the exciting liquids. They gave a very feeble current and the carbon was soon polarized; the sulphite of zinc formed also adhered to the zinc and prevented further action.

Ex. No. 14. Iodide of potassium saturated with iodine was tried; this also gave a feeble current and the carbon soon became polarized.

Ex. No. 15. A cell of the Maynooth battery was fitted up and a saturated solution of potassic bichromate in nitric acid used as the absorbing liquid; the battery was not very constant, and the iron was soon attacked; no fumes, however, were given off The electro-motive power was about 55 of a Daniell's cell.

The result of these experiments seem to show that the battery used in experiment No. 7 is the best for ordinary use, since it costs but little, if any more, than the Bunsen battery charged with nitric acid alone, and is entirely free from fumes until exhausted. If the following directions are observed in preparing the fluids, it cannot fail, I think, to give satisfaction.

To prepare the exciting liquid, sulphuric acid of 1·84 sp. gr. is mixed with nine times its volume of water and allowed to stand until the precipitated lead has all settled. The clear acid is then decanted and is fit for use. This plan of preparing the acid has been in use in this laboratory for some years and gives very good results, local action being almost entirely prevented by the removal of the lead.

To prepare the absorbing fluid, ordinary commercial nitric acid is saturated with potassic bichromate; this should be done in a warm room, as it takes up much more when warm than when cold. The solution thus prepared is mixed with onethird of its volume of sulphuric acid and enough water added to re-dissolve the chromic acid precipitated.

Two objects are gained by adding the sulphuric acid. The mixture is less expensive than if pure nitric acid is used and the internal resistance is decreased. If the internal and external cells are properly proportioned this battery will run until the exciting fluid is exhausted, without giving off any fumes of nitrous acid. If crude chromic acid could be obtained at a sufficiently low rate, No. 9 would be a very powerful and convenient battery for many purposes.

My thanks are due to Dr. Wolcott Gibbs for many valuable suggestions made during the progress of this investigation and for the use of the apparatus employed.

Cambridge, Jau. 17, 1871.

AM. JOUR. SCI.-THIRD SERIES, VOL. I, No 4.-APRIL, 1871.

ART. XXXVI.-Notes on the Geology of Santa Domingo; by WM. M. GABB.

ALTHOUGH the geological survey of the Republic of Santa Domingo has now been in progress about two years, nothing has been made public of our results, and I had not intended to publish anything until its completion. But circumstances now transpiring render it advisable that I should put on record at least a sketch of the principal conclusions arrived at.

The Republic is of a very irregular triangular shape, nearly twice as long east and west as from north to south. The total area is about 20,000 square miles. Running nearly through the middle, with a direction a little south of east, is a high chain of mountains, some peaks reaching a height of 9,000 feet. This range falls to the eastward, forming ultimately a chain of hills which runs parallel with the southern border of Samana bay. In some places it is hardly ten miles wide, in others (near the middle) it reaches a width of nearly forty miles, including its greater spurs. South of this range, bordering the coast, is a tract, partly of rolling hills, partly of plains, which, especially in the large peninsula at the eastern end, constituting the Province of Saybo, are broad grassy prairies, cut up by lines of trees, filling depressions and bordering water courses.

Parallel with this great range and bordering the north coast is another mountain chain, neither so broad nor so high as the first. This extends from Manzanilla bay, almost on the Haytien frontier, to the extreme end of Samaná peninsula. It is cut through, near the head of Samaná bay, by a narrow belt of marsh land, through which runs a salt water creek, thereby making Samaná really, an island. This range has a few peaks rising to 2,500 or 3,000 feet and is nowhere much over ten miles wide. Between the two mountain chains lies a long valley having an average width of ten or fifteen miles, in some places much wider, in others, encroached on by the foot-hills of the mountains on its south. The valley is divided near its middle by a water-shed, but 500 feet above the sea. The Yaqui and Yuna rivers, rising in the higher hills south, run through this valley, the former emptying into Manzanilla bay on the west, the latter into Samaná bay on the east. On the south side of the island are several large rivers which run from the same mountain southward. The principal of these are the Macorio, Ozama, Jaina, Nigua, Nizao, Ocoa and Neyba, the last sometimes called the Yaqui of the south, rising in the same peak as its northern namesake.

Having thus described the leading topographical characteristics as concisely as possible, we can more easily explain

the geological features which are intimately connected with them.

The great central chain of mountains consists of an immense cone of syenite and syenitic rocks, evidently of later date than the metamorphic strata that flank it. This mass is probably, in some places, as much as fifteen or twenty miles wide, though its southern and southwestern borders have not yet been explored, lying as they do in the Province of Azua, to which our labors have not yet extended. In this Republic it makes its appearance on the borders of Hayti, about fifteen miles south of Manzanilla bay, and from here makes all of the higher range of central mountains, to a point just about due northwest of Sta. Domingo City, or in other words, the center of the Republic; there its northern boundary suddenly bends south, becoming the eastern, the mass making a tongue eighteen to twenty miles wide, running a little east of south, to a point about twenty miles from the coast and nearly north of Bani. From analogical reasoning, based on the character of its northern margin and the peculiarities of the topography, it is almost safe to predict, that north of Banica and San Juan, or in other words in the mountains of the north-west, it will not have a much greater width than the strip above Bani. This mass of crystalline rocks has pushed up, tilted, folded, and in some places sent complicated net works of dikes into the overlying strata. Some of the dikes extend miles from the parent mass, and are of all sizes from 100 feet and upward, down to a thread. The lithological characters of the syenites are not so variable as might be anticipated over so wide an area (say 20 by 100 miles). The rock is usually a light gray, moderately finegrained mixture of the ordinary constituents, quartz, feldspar and hornblende, in nearly equal proportions, though sometimes the latter mineral makes up almost the entire mass, in the shape of large crystals, and more rarely it is almost entirely absent, and still more rarely a little mica occurs. No gneiss has been observed, but two or three localities of mica slate have been found, and one or two erratic pebbles have been discovered composed of quartz and feldspar only.

Overlying the syenite, and as stated above, uptilted by it is a heavy deposit, several thousand feet thick, of conglomerates, jaspery and magnesian slates, with a little limestone. These are almost invariably metamorphosed to such an extent as to have entirely destroyed their original character, and often, even their stratification. In the country west of Bani, both about the lower Ocoa and farther north, the shales are so little altered that they can be recognized as fissile clay shales, in a few cases giving rise to salt springs, but in no case fossiliferous. I was fortunate enough, at one locality on the Nigua, to discover a small locality in the limestone, almost unaltered and with a few

fossils, usually poorly preserved. I succeeded in obtaining a little Ammonite, a Trigonia, a Pterocardia shell, besides a few less characteristic genera, and what may prove to be a Baculite !; thus fixing the secondary and possibly the Cretaceous age of the oldest stratified rocks on the island.

These rocks form a border to the crystalline cone, and extend to the eastern end of the island forming its "backbone." On the borders of the syenite, it is often cut by veins of auriferous quartz, and elsewhere it contains unimportant deposits of copper, and in one locality, iron.

In the neighborhood of San Cristobel, twenty miles west of Sta. Domingo, and extending as far west as we have explored, are small isolated basins of the next formation. This obtains its greatest development on the north side, but is said also to fill a depression extending to Port au Prince. I refer to the Tertiary rocks, which play an important part in the geology of the Island. They lie unconformably on the edges and flanks of the secondary deposits, fill all of the great northern valley of the Citao, and constitute the northern chain. In the northern foot-hills of the central chain, these rocks come in as a thin edge, gradually thickening as we descend into the valley, and eventu ally acquire a thickness of perhaps 1,500 or 2,000 feet. They consist of conglomerates, sandstones, gray, blue, brown and white shales, argillaceous and pure limestones, the rocks being enumerated in an ascending series from the conglomerates upward. Fossils are found throughout the series, though usually rare except in the blue and brown shales where they are sometimes very abundant, and in an extraordinarily beauti ful state of preservation. There have been enough fossils found in all the beds, from base to top, to settle the question, that no line of demarcation of age can be drawn in the series. The species have not been sufficiently studied, by me, to enable me to express a positive opinion as to the part of the Tertiary group to which they belong. Messrs. Geo. Sowerby (Quart. Jour. Geol. Soc., London, 1849, p. 44), and J. Carrick Moore, (loc. cit. and Quart. Jour., 1853, p. 129), consider them, for good reasons given, to be Miocene, in which opinion I am inclined to concur; while Mr. T. A. Conrad, whose acquaintance with the American Tertiaries is greater than that of any other person, says they are Oligocene.

In the valley of the Cibao these beds are but little disturbed, at most being but slightly undulated; but in the northern range of mountains they are in some places highly uptilted, in one locality being vertical, but were much folded. The coal mines reported to exist in Sta. Domingo are merely the beds of lignite in the shales of this group.

It is proper here to call attention to an article in the Quart Jour. Geol. Soc. 1853, p. 115, et seq. by a Mr. T. S. Heneken, illus

trated by a map and several sections. I do so because the above description is totally at variance with the article quoted, and these examinations were made with a full knowledge of the statements of Mr. Heneken. I make this explanation, not from any feeling of antagonism, and may mention that the author died several years ago on this island; but a regard for truth requires me to state that the descriptions there given of the geology of the Cibao are, at least, very extraordinary. Among other things, he has taken a part of the Tertiary sandstones, erected them into an older formation, and states, incorrectly, that it underlies unconformably the blue fossiliferous shales. Another important inaccuracy is his assertion that the north range, at Mt. Muraso, is an anticlinal of older rocks (see fig. 3, p. 119, loc. cit.); whereas it is really the newer part of the Tertiary deposit, lying at low angles, the anticlinal being far north of the summit of the mountains. The errors arose without doubt from the inexperience of the observer.

Bordering almost the entire coast, from Manzanilla bay, around the eastern end of the island to the north of the Nizao river, on the south side, is a deposit of horizontal limestone of very modern origin, in places full of living corals and very imperfect casts of living species of mollusca, but more usually, where not hardened by the weather, a white or cream-colored friable limestone, the result of the breaking down or decomposition of coral. It rarely makes bluffs on the coast of more than 20 or 30 feet in height, but has been penetrated by wells between 150 and 200 feet deep without passing through it. This border has a variable width of from a few hundred yards to many miles, and in the neighborhood of Sta. Domingo City, where it is a dozen miles wide, it illustrates beautifully the phenomenon of change in lithological character of the same beds. Toward its margins in this vicinity near what was at that epoch the mouth of the Jaina river, a few pebbles begin to appear, unmistakably attributable to the hills of the upper Jaina. Proceeding northward, or toward the former coast, these pebbles become more numerous and the lime less pure, until eventually the same stratum can be traced into a common shore gravel, evidently the product of the river, and without a perceptible trace of lime. Further; in going east from the neighborhood of the Jaina, but along the ancient coast, the pebbles again disappear and the shore margin of the deposit becomes, as might be anticipated, sand; while farther out the limestone belt continues in the position of the former reef.

No volcanic rocks have been encountered in the course of our explorations except in the mountains north of Bani, where we found a single dike of black porphyry with large white crystals of feldspar.