Webster condenser, but of 110°, perfectly achromatic and adjustable for thickness of the glass slide, and mounted over a graduating diaphragm, a pair of shutters for an adjustable horizontal slit (one of them, or another single shutter, capable of moving independently for oblique illumination), and a graduating centre stop capable of stopping off from 25° to 80° of light, I believe that most persons who use the instrument for the ordinary investigation in natural history would consider the combination rather as a necessary part of their stand than as an accessory to be sometimes used with it.

Dr. WALKER of New Orleans, La., read a paper prepared by Professor EUGENE W. HILGARD, State Geologist of Louisiana, on "The Upper Delta Plain of the Mississippi." The paper is one of a series by the same au thor, the preceding ones having treated of the older formations which characterize the geology of the Great Enlargement of the Mexican Gulf Basin, of which the Mississippi River, below Cairo, forms the axis. We are first reminded of the successive disappearance of the slightly dipping formations, in proceeding south from Vicksburg. It is shown that the delta or alluvial deposits proper, cover the older formations to a comparatively slight depth only, the river running on paludal deposits, and then on an ancient sea bottom, of corresponding (late quaternary) age, from above New Orleans to near its mouth. It thus appears that Artesian bores in the vicinity of New Orleans, tubed through the (chiefly marine) deposits of the upper strata, and penetrating the great beds of Orange sand, or southern drift, will probably furnish an abundant rise of the best of water. The great torrent which produced the northern drift is seen to have swept over the southern coast with sufficient force to traus port pebbles of five to six ounces weight from far distant regions, the nearest being Tennessee and Arkansas. This great eroding agent seems also to have so cut and worn the older formations into ridges and channels, that the overlying ones vary greatly in thickness, while level at the surface. The singular phenomena known as the New Orleans Gas Wells, are also mentioned. When bores were sunk for water, the gas rushed up with such force as to carry up several cart loads of sand in a single night, and when the gas became ignited, it was extinguished with great difficulty.

An abstract of a second paper by the same author, "On the Mudlumps of the Passes of the Mississippi," was given by Prof. J. E. HILGARD. The Mudlumps are islands formed by upheavals of the bottom, off the mouths of the Passes, inside the bar. They often rise in mid-channel, obstructing navigation and diverting the current, and at times bringing up objects long ago lost from vessels. They form a number of pretty large islands, especially near the mouth of the South-west Pass. On them we frequently find springs of liquid mud, accompanied by bubbles of com bustible gas; these springs often exhibit all the phenomena of mud volcanoes-extensive cones of mud, with an active crater in the middle. Most of the material of the Mudlumps seen above water, bears evidence of having once belonged to active cones, now extinct.

The author investigated the origin of these springs, by an examination of their ejecta-gas, water, and mud. The gas he found to be such as is produced by vegetable matter in its first stages of decay. The mud contains evidence of a mixed fluviatile and marine origin; while the water in which it is diffused, has the composition of sea-water changed under the influence of ferrugino-calcareous river mud, containing fermenting vegetable matter.

The conclusion reached is, that the mud is the same as that which is deposited on the "blue clay bottom" of the Gulf, outside the bar, in a semi-fluid state. In its annual advance, the bar covers this mud stratum, which exists equally higher up the Passes; the increase in weight by vegetation, alluvion, etc., of the new formed land above, as well as that of the bar below the mouth, causes the bottom to bulge upwards at the points of least resistence, i. e. in the deepest channel.

Attention was called to the fact, that of all rivers known, the Mississippi is the only one exhibiting either mudlump action, or the peculiar narrow lands of bank, advancing rapidly towards deep water, which are known as "necks," and are obviously dependent on the mudlumps for their origin. It is therefore permissible to infer, not only that all the similarly shaped alluvions above the head of the Passes, at least as far as the forts, have been formed by mudlump action, but also that the latter will cease so soon as the bar, in its advance, shall pass beyond the shelf of "blue clay botton" (presumably of the Port Hudson age), into the deep water of the Gulf; which point is now nine miles out from the mouth.

Professor W. C. KERR read a paper on "A Point in Dynamical Geology." This paper called attention to the agency of the sun as a probable and sufficient explanation of the well-known remarkable coincidences of the coast lines, mountain systems and chains of islands, nearly all the great "feature-lines" in the physiognomy of the globe,-with the arcs of great circles tangent to the polar circles; the exceptions being generally arcs of great circles perpendicular to the former; inasmuch as the sun oscillates about (within 1° of) a position (± 22 1-2° declination), which is approximately polar to the above system of great circles, for more than one quarter of the year; and all the solar influences, mechanical (tidal), thermal, electromagnetic and chemical, being in full play for this long period, about this great dynamical plane which separates the luminous from the dark hemisphere, could not conceivably havę failed to exercise a profound influence in outlining the rising ("becoming ") features of the globe in its plastic and formative state. Similar considerations are applicable to the lunar influence, which was cumulative in the same direction.

THE ONEONTO AND MONTROSE SANDSTONE, ETC. - In the Report of my paper on the Oneonto and Montrose Sandstone etc., the language may convey the idea that the sandstones of both these localities have been identified with the Portage Group, which was not intended. The Oneonto Sandstone is pretty clearly an equivalent of the Portage Group of Central

and Western New York, while up to this time no positive determination has been matle regarding the Sandstone of Montrose. The latter may be the equivalent of the Red Sandstone of Tioga and of the summits of the Catskill, but we have not yet the facts necessary for the determination. Will you have the kindness to make some note of correction in the next number of the NATURALIST. Yours, etc. JAMES HALL.

The following papers were also read before the Association:

PAPERS READ IN SECTION B.-NATURAL HISTORY.

Notes on Granitic Rocks. By T. Sterry Hunt.

On the Oil-Bearing Limestone of Chicago. By T. Sterry Hunt.

On the Lignites of West America, their Distribution and Economic Value. By J. S. Newberry.

On the character of the Observations necessary to interpret the record of the last Glacial Period. By N. S. Shaler.

Microscopic Circuits of Generation: a. Of Zymotic Fungi: b. Of the (nominal) Genera of Fresh water Algæ, as development-phases of Bryaccæ, etc. c. Of Vorticello-Planarians. By T. C. Hilgard.

The Genetic Relations of the Arietes. By Alpheus Hyatt.

On the occurrence of native iron, not meteoric. By H. B. Nason.

On the salt deposit of Western Ontario. By T. Sterry Hunt.

On the Relation of Organic Life of the several continents to the Physical Character of those land areas. By N. S. Shuler.

The Development and Old Age of the Tetrabranchiate Cephalopods. By A. Hyatt. On a method of collecting certain Geological facts, adopted by the "Social Science Association." By N. S. Shaler.

On the Sequence and Chronology of the Drift Phenomena in the Mississippi Valley By J. S. Newberry.

BOOKS RECEIVED.

Archiv fur Anthropologie. Braunschwieg, vol. iv. Heft, 1, 2, 1870. 4to.

Observations on the Geography and Archæology of Peru. By E. G. Squier. London, 1870. 8vo. Feuille des Jeunes Naturalistes. Nos. 1-5. May to August, 1870. Dornach, Haut-Rhin. ($1.00 gold a year.) 8vo, pp. 8.

Report on the Mollusca of Long Island, N. Y., and of its Dependencies. By Sanderson Smith and Temple Prime. New York. 8vo, pp. 30. 1870.

Annals of the Lyceum of New York. pp. 345-376.

American Journal of Conchology. Vol. vi, part 2. November, 1870. Philadelphia,
Entomologist's Monthly Magazine. June, 1869-October, 1870. London, 8vo.

Seventh Annual Report of the Belfast Naturalists' Field Club. 1870. Belfast, Ireland, 1870. Svo, pp. 12, 25. Opening Address of Dr. Wyville Thompson, November 10, 1869, Belfast, Ireland, 4to. Proceedings of the Lyceum of Natural History. New York, April 4, June 6, 1870. Proceedings of the Academy of Natural Sciences. Philadelphia. 1870. pp. 93-108. American Journal of Microscopy. Vol. 1, No. 1. Chicago, November 1, 1870. monthly. $1.00. 4to, 2 columns. pp. 16.

American Bec Journal. November, 1870.

Published

Chemist and Druggist. October 15. London.

Bulletin of the Torrey Botanical Club. Vol. 1, No. 10. October, 1870.

Minerals of Colorado. By J. Alden Smith. Central City, 1870. 8vo, pp. 16.

Journal of Popular Science. Copenhagen, 1870. Vol. v, part 2.

Collections of the Minnesota Historical Society. Vol. I, part 1. St. Paul, 1870. 8vo.

THE

AMERICAN NATURALIST.

Vol. IV. - JANUARY, 1871. — No. 11.

THE ANCIENT LAKES OF WESTERN AMERICA: THEIR DEPOSITS AND DRAINAGE.*

BY PROF. J. S. NEWBERRY, LL. D.

THE wonderful collections of fossil plants and animal remains brought by Dr. Hayden from the country bordering the Upper Missouri have been shown by his observations, and the researches of Mr. Meek, to have been derived from deposits made in extensive fresh-water lakes; lakes, which once occupied much of the region lying immediately east of the Rocky Mountains, but which have now totally disappeared. The sediments that accumulated in the bottoms of these old lakes show that in the earliest periods of their history they contained salt water, at least that the sea had access to them, and their waters were more or less impregnated with salt, so as to be inhabited by oysters and other marine or estuary mollusks. In due time the continental elevation. which brought all the country west of the Mississippi up out of the widespread Cretaceous sea, raised these lake-basins altogether above the sea level and surrounded them with a broad expanse of dry land. Then ensued one of the most interesting chapters in the geological history of our continent, and one that, if fairly written out, could not fail to be read with pleasure by all intelligent persons. The details of

* From Dr. Hayden's forthcoming "Sun Pictures of the Rocky Mountains."

Entered according to Act of Congress, in the year 1870, by the PEABODY ACADEMY OF SCIMO, in the Clerk's Office of the District Court of the District of Massachusetts. 81

AMER. NATURALIST, VOL. IV.

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this history are however, in a great measure, yet to be supplied; inasmuch as the great area of our western possessions is still but very partially explored, and it is certain that it forms a great treasure-house of geological knowledge, from which many generations will draw fresh and interesting material before its riches shall be exhausted.

The enlightened measures adopted by our Government for the exploration of the public domain, the organization and thorough equipment of the numerous surveying parties that have traversed the region west of the Mississippi within the last twenty years, together with the more extensive explorations by private enterprise of our great mining districts, have resulted in giving us materials from which an outline sketch can now be made that may be accepted as in all its essential particulars, accurate and worthy of confidence.

It has happened to me to be connected with three of the Government surveys, to which I have referred, and to spend several years in traversing the great area lying between the Columbia River and the Gulf of Mexico. The observations which I have made on the geological structure of our Western Territories supplement, in a somewhat remarkable way, those made by Dr. Hayden, so that taken together, our reports embody the results of a reconnoissance stretching over nearly the whole of our vast possessions west of the Mississippi.

Our knowledge of the geology of this region has also been largely increased by the no less important contributions of other explorers. Among those who deserve most honorable mention in this connection are Mr. George Gibbs, to whom we are indebted for most that we know of the geology of Washington Territory; to Professors W. P. Blake and Thomas Antisell, to Prof. Whitney and the other members of the California Geological Survey; to Baron Richtofen, the lamented Rémond, Drs. Shiel, Wislizenus, and others.

The results obtained by the last, largest and best organized party which has been engaged in Western explorations,