downward, until, at a depth of about forty feet (B), it is ten feet wide. The whole of the space above this level is filled with the débris of the adjoining Mesozoic red shale, with occasional angular fragments of Auroral limestone, without any trace of organic remains. Where the cave narrows to ten feet (B) the floor is composed entirely of a black clay 18 inches thick, filled

Map of the region, showing the position of the Lime Quarries and cave; area lined vertically, is region of Mesozoic red shale; horizontally, of Auroral limestone; obliquely, of Primal sandstone.

with leaves, stems, and seed-vessels of Post-tertiary plants. Scattered all through this mass of vegetable remains, and also in a red tough clay underneath, for six to eight inches in depth, are found the fossils noticed in this paper.

The Mastodon is M. Americanus of Cuvier. One of the teeth measures sixteen inches in circumference; the enamel is white or cream-colored, and well preserved. The tusk was uncovered for three or four feet in length, and was from five to six inches in diameter, but crumbled into fragments on being moved. The large bones are light cream color, much decomposed, but some of the articulations are very distinct.

In addition to the Mastodon and Tapir, Prof. E. D. Cope and myself have determined Sloths of the genera Megalonyx, and Mylodon, a large Artiodactyle, an Equine animal, and a large bear, the full size of the grizzly, besides other species mentioned beyond. This bear is entirely distinct in character from existing species of North America and the northern regions of the old world, as well as from the cave bear of Europe. It has been described by Leidy from a single molar from South Carolina, and if of the true genus Ursus, as is probable, will stand as Ursus pristinus Leidy.

The bones of Megalonyx are some of them in an excellent state of preservation; the claws and other bones of the feet especially are exceedingly perfect. Several canine and molar teeth of Megalonyx, 1 by 14 inches, with the cement and crowns perfect, have been found.

Of Mylodon both bones with claws and teeth have been discovered; also teeth and bones of a large Tapirus, the teeth of which retain their white highly-polished enamel. The bones of both Mylodon and Tapirus are dark-colored, and the bone-cells usually filled with iron pyrites.

Section of cave and adjoining rock; M, Mesozoic shale; A, L., Auroral limestone.

There are rodents of the existing genera Hesperomys, Fiber, Sciurus, Lepus, &c. The reptiles are serpents, tortoises and batrachians of several species. A number of Coleoptera are fortunately preserved, several of them Carabidae. Several species of birds occur, including a turkey, snipe, &c.

The remains of Mylodon, Ursus and Tapirus have been mostly obtained from the tough red clay directly under the plant bed, but the remains of rodents, snakes, tortoises, birds, plants and insects, are entirely confined to the plant bed. Neither the bones or teeth are rolled or water-worn, but all are sharp and well defined.

As far as our investigations have progressed, the cave has now afforded us the following species:

Mastodon Americanus Cuv., 1; Mylodon, 1; Megalonyx, ?2; Tapirus, 1; Equus, 1; an undetermined ruminant; an undetermined carnivore; Ursus pristinus, and another undetermined species, 2; ? undetermined Bat; Lepus, 1; Arvicola, 1; Sciurus, 1; Fiber, 1; Hesperomys, 1; ? undetermined rodents, 2; Coluber, 2; Tropidonotus, 1; Crotalus, 1; Cistudo, 2; Rana, 1; ? Turkey, 1; Snipe, 1; making in all, 27.

Vertebrates, 27; Coleoptera, 10; Plants, 10; total, 47 species. Phoenixville, Pa., February, 1871.

ART. XXXIV.-On the Geology of the Delta, and the Mudlumps of the Passes of the Mississippi; by EUG. W. HILGARD.

[Read before the American Association at its last meeting in Troy.]

In previous papers* read before this Association, I have communicated the results obtained during two successive geological expeditions to Louisiana, so far as the more ancient formations are concerned. It is the object of the present communication to present and discuss the phenomena of that portion of the territory explored by me, lying within what is usually considered the alluvial area proper, or Delta, of the Mississippi river. Most of these observations were made in 1867, during the first of these excursions referred to, under the auspices of the Smithsonian Institution; their publication having been. delayed in consequence of want of time, on my part, to carry out the large amount of chemical and microscopic work involved in the discussion, which is even yet far from being as full as would be desirable. I hope, however, to be enabled, hereafter, to continue the investigation of the subject, both in the field and in the laboratory.†

I. The Upper Delta Plain.

I recall to mind the fact that, as we descend the Mississippi, the older strata successively sink from view. A few miles below Vicksburg we lose sight of the older Tertiary. Thence down to the latitude of Tunica Bend, La., we find the rocks of the Grand Gulf (Tertiary) age, possessing but a very faint southward dip. Next, the oldest representative of the Quaternary epoch, viz., the stratified Drift or Orange Sand, disappears beneath the water's edge near Port Hudson; while the swamp, lagoon and fluviatile beds, which have given notoriety to the latter locality, are seen above high water level not much farther south than the city of Baton Rouge.

The gradual descent and successive disappearance of these strata is not, however, altogether a phenomenon of dip, in the

*This Journal, II, vol. xlvii. Jan. 1869; Ibid., xlviii, Nov. 1869.

For material assistance in the investigations embraced in this paper, I am especially indebted to the officers of the Delta Survey in charge of the Coast Survey schooner Varina-Messrs. F. P. Webber and Henry L. Marinden, for reports of observations and specimens furnished; to Capt. Day, in command of the same vessel, then moored at the Head of the Passes, for a boat's crew and personal assistance in the examination of the mudlumps; to Mr. Moulton, of the Cromwell line of steamers; to Captain Ed. Yorke, of the Towboat Association, and to Capt. Andrews, then of the dredgeboat at the Southwest pass, for free transportation on their respective vessels; and to Capt. Tilford and other gentlemen of the N. O. Pilot Association, for generous hospitality as well as much valuable information. For similar favors I am indebted to Dr. Copes, President of the N. O. Acad. of Sciences, as well as other members of that body. Other acknowledgments will be found in their proper places.

usual sense, but in a great measure the result of consecutive deposition; while the surface slope of the Port Hudson deposits is manifestly in a great degree due to denudation, and in part, no doubt, to deposition on a sloping bottom. At Port Hudson as well as elsewhere, where extensive profiles can be seen, the deposits of that era exhibit the basin shape; both on the large and, sometimes, on the small scale. In this as well as in their lithological and paleontological features, they greatly resemble deposits now forming over large areas; and where the two are in juxtaposition, it is often difficult, sometimes impossible, to draw the line between them, since qualitatively their process of formation has been manifestly the same. Both above and below Port Hudson, and down as far as Fort St. Philip, the apparently alluvial river banks frequently exhibit at low water edge, solid blue clays, with cypress stumps and twigs imbedded therein, scarcely distinguishable from some materials occurring at Port Hudson, Côte Blanche, and other localities of the Port Hudson age; and as neither can be expected to contain any but living organisms, it is, thus far, from general considerations alone, that we can hope to deduce their real age. It might seem, at first sight, that the distinction is practically of little moment; but when it is considered that the Port Hudson deposits are separated in time from those of the present era, by a large portion of the "Champlain" period of depression, plus the entire "Terrace" period of elevation, it becomes obvious that the distinction is one of no little theoretical, and some practical, interest. For while the Port Hudson strata yield to the augur almost invariably a considerable rise of artesian water, no such result can usually be looked for in either river or delta deposits.

I think that a retrospective view of the geological history of the lower Mississippi Valley and Gulf Coast, as developed by my observations in the States of Mississippi and Louisiana, will serve to show the probability that by far the greater portion of what now constitutes the alluvial plain of the lower Mississippi is covered by the river deposits to a comparatively insignificant depth only; excepting where the ever shifting river channel itself has caused an unusual depth by excavation and subsequent filling up.

I have shown that toward the close of the Drift period, the place of the present Mississippi was occupied by what, but for its stupendous proportions, might be termed a torrent of fresh water, having, even as far south as the present coast line, a velocity sufficient to transport pebbles of five to six ounces weight, from localities not nearer than Tennessee and northern Arkansas; together with the smaller ones derived, doubtless,

from the same sources as the drift boulders of Missouri and Illinois.*

In the bored wells of Calcasieu, these pebbles have been found as much as 450 feet below tide level; the inevitable inference being (provided the sea level remained constant), that, since the time of their transportation, the coast has suffered a depression to at least that extent-in matter of fact, probably, fully twice that amount. The thickness of the drift stratum is about one hundred feet, the materials growing finer toward the top; indicating, therefore, a diminished velocity of the depositing current.

Overlying this sand and pebble drift, we find, as at Port Hudson, alternating strata of more or less lignitiferous clay and sand, 350 feet thick; a 130-foot clay bed lying on top. In its uppermost portion, this bed recalls to mind at once the variously colored clays of the Côte Blanche profile, with their calcareous concretions; but here, according to the concurrent testimony of the inhabitants and the microscope, marine shells take the place of the fresh-water fauna observed at the former locality. The sands which, on the whole, predominate in the lower portion, are readily distinguished under the microscope from those of the drift, by the predominant sharpness of the grains, and the occurrence of particles of lignitized wood; but I have not thus far succeeded in finding in them any other organisms. They resemble strikingly the materials obtained at corresponding depths in the bored wells in the city of New Orleans.

Few deep wells exist near the coast, in the interval between that city and the Calcasieu bores. In the only one of which I possess definite data, viz., at Salt Point on Bayou Salé, a bed of marine shells was found after passing through the first clay bed, at 60 feet.

* Miss. Rep, 1860, p. 26 and ff.; this Journal, II, May, 1866; and Nov. 1866; Ibid. Jan.. 1869; Ibid. Nov., 1869.

The magnitude of this phenomenon would give it a continental significance even if it were confined to what I have termed the "Orange Sand delta," below Cairo. But as I have elsewhere stated, similar pebble streams, with slack water deposits of ferruginous sauds intervening, exist in Texas; and I have the satisfaction of adding to the array of facts heretofore presented in connection with this subject, the testimony of Prof. Safford, of Tennessee; who, upon discussion, finds that the phenomena presented by the "Bluff gravel," "Ore region gravel,' and Eastern gravel" of this report, are most satisfactorily accounted for, and brought under a common point of view, upon the basis set forth in my publications, above referred to.

In connection with Tuomey's and my own observations in Alabama, and farther east, those of Prof. Safford acquire additional significance, and the southern stratified drift an additional claim upon the serious attention of American geologists. Compare Prof. Newberry's interesting paper on "The Surface Geology of the basin of the Great Lakes, and the Valley of the Mississippi," where it is stated that "no deposits, corresponding to the drift of the northern and western states, exist south of the Ohio river." (Ann. Lyc. Nat. Hist., N. York, ix, 213, 1869). This Journal, II, Nov., 1869, p. 335.