Air remaining (measured), 26 cc. 11° temperature and 756-8 mm. barometric height. A determination of silica was made from the liquid remaining in the bulb. Si=1648; theory=16-38. The density of the hexethylic disilicic ether is at 0° =1.0196, at 19°.2 =1·0019. The ether is a colorless liquid of slightly oily consistency, with a rather agreeable odor, scarcely differing from that of the normal silicate. It burns with a smoke composed of silicic acid like all of this class of compounds. Aqueous alcohol transforms it into products having a higher boiling point. It is not so easily acted on by moisture as the normal silicate. After we had demonstrated the existence of the above body we attempted to obtain the bisilicate of Ebelmen in order to determine whether it corresponds to the first anhydrid of silicic acid or to the second anhydrid of disilicic acid, if this latter exists; but all the experiments undertaken failed to give this body, whose existence seemed so probable on theoretical grounds and whose preparation seemed so easy according to the statements of Ebelmen. We have submitted to a great number of frac tionated distillations in the air, under a diminished pressure and in vacuo, the products boiling above 240°, without being able to observe any point, at which a particularly large quantity distilled; and it will be seen by our analyses, that the quantity of silicic acid contained in the higher products, was greater than that required by theory for the bisilicate of Ebelmen. The temperature also, which was measured in vacuo by a mercury thermometer, corresponds to 450° in the air, a point much higher than that at which Ebelmen supposed his compound to boil. It may be of use to give the results of our experiments as they teach us something concerning the nature of the condensed silicates containing more silicic acid than the ether just described. In order to determine the difference in boiling point due to a diminution of pression, and to ascertain what reliance could be placed on the constancy of boiling points in vacuo, we distilled, under a pressure of 3-5 millimeters, the normal silicate of ethyĺ having a fixed boiling point at 165°.5 in the air. Platinum wire and a piece of charcoal were put in the flask to make the ebullition as quiet as possible, but without any very marked effect. The normal ether began to boil at 55° and the thermometer rose rapidly to 72°-73° and remained nearly stationary at this temperature (in another experiment at 74°-75°) during the distillation. When the distillation was interrupted and recommenced, ebullition commenced always at a much lower point than 73°. According to this, the diminution of pressure to 3-5 mm. lowers the boiling point of the ether in question from 165°5 to about 73°. We have seen that the hexethylic disilicic ether, which distilled at 233°-8°, in the air distilled at 226°-230° under a pressure of 3-5 mm. For this latter product, the limits of temperature within which the thermometer varies during a distillation in vacuo, are much less than for normal ether. The ebullition is much more regular under a somewhat greater pressure, and for this reason and also because we hoped that the change of pressure might facilitate the separation of the products, as Roscoe has observed in the case of hydrates of acids, we made another series of distillations under a pressure of 60 millimeters of mercury. These distillations were made with an apparatus which permitted us to operate almost as rapidly as when distilling in the air, and it only requires a small hand pump, when no better is to be procured. B The opening B has an india-rubber tube through which is passed the glass tube leading from the flask containing the substance. At C a thermometer is introduced in the same way. The lower end, A, of the receiver has a tube, which is closed during the distillation, and is opened to draw off the product when required. It is not necessary to surround the receiver with water, as the specific heat of the silicic ether is very small. The opening D, which is closed with a piece of glass rod fitting into an india-rubber tube, serves to add a new quantity of liquid when required. The object of the other parts of the apparatus is obvious. The balloon at the extremity only serves to augment the volume, so that a constant pressure may be more easily obtained; its communication with the distilling apparatus is closed when it becomes necessary to open the latter. All the connections were made with india-rubber tubes boiled in potash, and used double, the inner one coated with tallow, and when the apparatus was left to itself the pressure only va ried a few millimeters in twenty-four hours, and could easily be kept perfectly constant by a few strokes of the air pump during a distillation. We will give the results of several series of distillations made with the same material under different pressures. [To be concluded.] ART. XVIII.-Remarks on the Cretaceous rocks of the West known as No. 1, or the Dakota Group; by F. V. HAYDEN. THE Cretaceous rocks of the Upper Missouri have been separated into five divisions, which have been designated, for the sake of convenience, by Nos. 1, 2, 3, 4, and 5.* They have also received special geographical names indicating points where they are shown in their largest development. The Dakota group or Formation No. 1, lies at the base of this series, and either as an outcropping or underlying rock extends over a large portion of Nebraska, Dakota, Minnesota, Kansas, and even reaches far southward into New Mexico. It is more distinctively defined along the Missouri river between Omaha City and the Big Sioux, where it exhibits its typical characters. The lithological characters of this group have been so often described in former memoirs by Mr. Meek and the writer, that they scarcely need to be repeated here. The principal object of this article is to present such additions to our knowledge of it as may have been obtained since our last papers were pub lished. It is not intended to discuss in detail any differences of opinion, or to make any criticisms, but to present certain facts and statements gathered by Professors Capellini and Marcou in their tour to Nebraska in 1863, and the results of the investigations of Prof. Heer derived from the study of the flora of this group. * Memoirs Am. Acad. Arts and Sci., vol. v, new series, also numerous papers by F. B. Meek and F. V. Hayden. + Proceedings Acad. Nat. Sci., Dec. 1861. In order that the geological relations of the Dakota group may be better understood, I have given a brief summary of the contiguous formations. In ascending the Missouri river we find near Fort Leavenworth exposures of limestone which, up to the present time, we have regarded as belonging to the upper Coal-measures. The beds are all nearly horizontal, with a slight, almost imperceptible, dip toward the northwest. As we continue up the Missouri, layer after layer of these Coal-measure rocks pass from view beneath the water level of the river, and when we reach Fort Lisa they have entirely passed from sight and are overlapped by a bed of variegated friable sandstone. The sandstone undoubtedly exists, or has existed, as an underlying rock considerably lower down the river than Fort Lisa, probably nearly to Omaha City, but has either been removed by erosion, or concealed by the great thickness of superficial recent deposits which cover this country, sometimes entirely hiding from view the underlying basis rocks over large areas. Ascending the Platte valley we have the true Upper Carboniferous limestone nearly to the mouth of the Elkhorn. Before reaching that point, however, we observe a portion of No. 1 resting directly upon the limestones, as the following section will show. 1. Gray compact siliceous rock, passing down into a coarse conglomerate, an aggregation of water-worn pebbles, cemented with angular grains of quartz; then a coarse grained micaceous sandstone (lower portion of Dakota group), 25 feet. 2. Yellow and light gray limestone of the upper coal-measures containing numerous fossils, Spirifer cameratus, Spirigera subtilita, Fusulina cylindrica, Productus, Chonetes, and abundant coral and crinoidal remains.* At the mouth of the Elkhorn, the Carboniferous limestones have passed from view beneath the Cretaceous sandstones. The intermediate Permo-carboniferous and Permian rocks, as well as the variegated and gypsiferous marls and clays which are quite conspicuous westward from Fort Riley, are wanting in this region. The Dakota group as seen along the Missouri passes beneath the bed of the river about 30 miles above the mouth of the Big Sioux. How far up the Big Sioux it extends is not yet known; but at a point 40 miles up the valley, the seam of earthy Lignite, which is seen just above the Omaha reserve, crops out, and is exciting some attention among the farmers. The researches of Prof. Hall have extended this group northward from the Missouri river into Minnesota 130 miles or more. In an interesting memoir read before the American Philosophical Society at Philadelphia, Prof. Hall, after describing numerous exposures of the variegated quartzites from St. Peters to Fort * Trans. Amer. Phil. Soc. 1861. Ridgely, says: "Proceeding westward from Fort Ridgely, I had no opportunity of seeing any other formation than the prairie for about thirty miles. At this point near where we crossed the Big Cottonwood River, there is an exposure of rock in the bank of the stream; and at a short distance farther on, some explorations had been made for coal, and a shaft had been sunk to the depth of more than one hundred feet. The materials thrown out of this shaft consisted of a dull greenish argillaceous sand, with calcareous nodules, together with irregularly laminated sandstone containing vegetable remains. The order of deposits, as given to me by Mr. Morin, who superintended a part of the working, was as follows: 1. Ironstone; 1 ft. 6 inches. 2. Sand, clay, etc.; 40 ft. 3. Earthy coal;* 1 ft. 8 inches. 4. Sand, clay, etc.; 3 ft. 5. Sandstone in irregular and diagonally laminated layers, with sometimes calcareous concretions, and containing plant remains; 5 ft. 6. A Calcareous sandy clay of variable color and character; 20 ft. 7. Sandstone in loose thin layers of three or four inches; 4 ft. 8. Clay with coaly seams near the bottom; 16 ft. 9. Clay; 13 ft. 10. Loose quicksand to bottom of shaft. "In the river bank, at a quarter of a mile distant, and at a level 30 or 40 feet below the ground where the shaft began, there is the following exposure: 1. Loose ironstonet in nodules and irregular concretions, more or less mixed with drift and pebbles; 1-2 ft. 2. Calcareous clay; 6-8 ft. 3. Earthy coal; 8 inches. 4. Clay as above coal; 4 inches. 5. Yellow or ferruginous sand and clay; 3-3 ft. 6. Ferruginous sandstone in irregular layers and diagonally laminated to level of river; thickness unknown. "This sandstone appears to be the same as that containing the vegetable remains met with in the shaft; and though I did not find plants in it at this point, I was informed that specimens had been found there; and at another place on the Cottonwood I found them to be quite common. Near the previous exposure, 26.1 * An analysis of this coal, by Prof. T. Sterry Hunt, gave the following results: 25.7 48.2 100.0 In the sections of strata near the mouth of the Redwood river, there is a stratum of similar earthy coal three feet thick. This ferruginous layer does not appear to belong to the regularly stratified deposits, as it overlies, irregularly, the edges of the successive beds, and has been deposited after the denudation had taken place. AM. JOUR. SCI.-SECOND SERIES, VOL. XLIII, No. 128.-MARCH, 1867. |