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recent writer' claims that the tops of the Boston Mountains represent a peneplain, and cites as evidence the fact that they correspond very closely in height with the Ouachita Mountains south of the Arkansas valley. This evidence is given on the assumption that the rather uniform height of these mountains represents a peneplain; but this is a hypothesis far from being established. Mr. L. S. Griswold, in his work on the novaculite region of Arkansas, encountered the problem of the nonconformance of some of the main streams of the region to the structure and topography, to account for which he presents the theory of a post-Carboniferous base-level, on which was subsequently deposited Cretaceous strata.2 If the present writer correctly interprets Mr. Griswold, he believes the south-flowing streams, which form water-gaps in some of the highest mountains of the region, are superimposed streams, their courses having been determined by the slope of the Cretaceous area after elevation. Mr. Griswold does not claim that the evidence of this is conclusive. It is the opinion of the present writer, from somewhat limited observation, that the even crests of the Ouachita Mountains are due to structural and lithological conditions and not to base-leveling. But were it established that they represent a peneplain, the fact that the Boston Mountains closely agree with them in height does not argue a peneplain for the latter. The one is a folded area, and the other an area of horizontal rocks (Fig. 2). Erosion in the one has resulted in wide, anticlinal valleys through which flow sluggish streams, while erosion in the other is in its early stages. It would seem to follow that the time of elevation of the one region is far antecedent to that of the other, and consequently the correspondence in height between the two only accidental.

If, however, we look to the north of the Boston Mountains, we find conditions which seem to throw some light upon the subject. As has already been said, this is a region of great denudation. Its general elevation is from 700 to 1000 feet

'O. H. HERSHEY, Am. Geologist, Vol. XXVII, No. 1, pp. 25 et seq.

2 Ark. Geol. Surv., 1890, Vol. III, pp. 220.

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FIG. 2- North-south section of the Boston Mountains and adjacent regions, near Arkansas-Indian Territory line.

lower than that of the Boston Mountains. Its streams are mature, the valleys comparatively wide, and the topography in general presents the aspect of much greater age than that of the Boston Mountains. Professor C. F. Marbut, in discussing that part of this region which lies in Missouri, claims. that it was base-leveled in early Tertiary times, and the present cycle of erosion was instituted by an elevation which dates from middle or late Tertiary times. Be that as it may, the question as to whether the region to the north of the Boston Mountains ever suffered denudation to the extent of base-leveling does not particularly concern us here. The fact of interest is that the denudation of the extensive region to the north has been very great and the topography is old, while that of the Boston Mountains is limited and the topography young.

It would appear that this difference in topography cannot be attributed to the massive beds of sandstone at the top of the Boston Mountains, for these same beds, while they have doubtless had a great deal to do with preserving the region, formerly extended over much if not all the denudated area to the north. Besides, if we attribute the preservation of these mountains to the character of the rocks composing them, we are encountered by the question as to why erosion has been so extensive to the north of the region, removing the rocks over a large area, leaving only here and there hills or circumdenudation, while in the southern part adjacent to the Arkansas valley it has scarcely begun.

I am able to account for the great difference in the stages of erosion in the two regions only by conceiving the Boston Mountain area to have been at a lower elevation than the area to the north during Mo. Geol. Surv., Vol. X, pp. 27-29.

the time the extensive denudation was going on over the latter. So low must it have stood that the strata now composing their summits suffered but little erosion, while the same beds extending northward suffered much because of their greater height. If this be true, the actual amount of degradation suffered by the Boston Mountain region is indeterminable; but as there was more or less of it, and the region stood at a low level, it would be considered a peneplain. The elevation, which must have occurred in late Tertiary or in post-Tertiary time, was greatest along the present east-west axis of the plateau, gradually decreasing to the northward, and changing the region from a low, monotonous plain to a plateau approximating 2,500 feet in height, greatly modifying the former drainage and instituting that of the present.

Aside from the difference in topography between the region under discussion and the one to the north, the writer cannot at present claim very great support for the idea herein presented. There are, however, some other facts that seem to lend the hypothesis support. (1) The region being on the border of the Ozark uplift, it is probable that during the greater part of its history it lay at a low level and consequently suffered comparatively little from erosion. (2) The outliers of the Boston Mountains to the north are as a rule lower than the main plateau, though capped by the same rocks, thus indicating an axis of elevation to the south of the outliers. (3) The eastward course of White River and its tributaries may be due to their having been diverted from what would seem a more natural southern course, at the time of the uplift.

UNIVERSITY OF ARKANSAS,

Fayetteville, Ark.

A. H. PURDUE.

THE DISCOVERY OF A NEW FOSSIL TAPIR IN

OREGON

A FAIRLY complete phylogenetic series of early Miocene tapirs has been made known to science through the researches of Messrs. Wortman, Earle, and Hatcher." Between these ancestral forms, referable to the genus Protapirus, and the living species is a gap in the line of descent which has remained unbridged until the fortunate discovery of the form presently to be described.

Our knowledge of the tapir phylum since the White River epoch may be summarized in a few words. In 1873, Dr. Joseph Leidy 3 described under the name Lophiodon oregonensis, two imperfect superior molars obtained by Professor Thomas Condon at Bridge Creek, Oregon. Two species have been described by Professor Marsh, which he refers to the genus Tapiravus: T. rarus from the Loup Fork of the Rocky Mountains, and Tapiravus validus from the Miocene of New Jersey. From the brevity of the description and the lack of figures, these species are practically indeterminate. Remains of tapirs belonging to the existing genus are known from the Quaternary gravels of California,5 and have been described from several localities in the eastern states.

During the summer of 1900, Professor John C. Merriam and Mr. V. C. Osmont, of the University of California, while collecting in the fossil beds of the John Day valley, Oregon, obtained J. L. WORTMAN and C. EARLE, "Ancestors of the Tapir from the Lower Miocene of Dakota," Bull. Am. Mus. Nat. Hist., Vol. V, p. 159.

J. B. HATCHER, "Recent and Fossil Tapirs," Am. Jour. Sci., 4th ser., Vol. I, p. 161, 1896.

3 U. S. Geol. Surv. of the Territories, Vol. I, p. 219, Pl. II, Fig. 1.

4O. C. MARSH, Am. Jour. Sci., Vol. XIV, p. 252, 1877.

5 J. D. WHITNEY, "Aurif. Gravels," Mem. Mus. Comp. Zool., Harvard, Vol. VI,

p. 250; W. P. BLAKE, Am. Jour. Sci. Vol. XLV, p. 381.

the bones which form the subject of the following discussion. The remains are from the Promerycochoerus horizon (Upper John Day) exposed on the bank of the John Day river, beneath the Columbia basalt, to the west of Spray post-office, Wheeler county, Oregon. In a recent paper,' Professor Merriam named the beds of the Upper John Day the Paracotylops beds, basing the name on the new genus Paracotylops, proposed in the same paper by Dr. W. D. Matthew for the typical Oreodonts of this horizon. In the numbers of the American Journal of Science for last December and January, a paper by Mr. E. Douglass appeared in which these Oreodonts were provisionally named Promerycochorus. Neither Professor Merriam nor Dr. Matthew read this article before the publication of Professor Merriam's paper, and consequently did not notice the new name. It now appears that Promerycocharus should be retained as a generic name, and consequently, at Professor Merriam's suggestion, the name of the beds of the upper division has been changed from Paracotylops to Promerycochoerus beds.

The type specimen (No. M 934, Univ. of Cal. Pal. Mus.) comprises several superior incisors; the lower jaw lacking the posterior portion, with representatives of all the inferior dentition excepting the canines and the third molar; the proximal portion of the left humerus; the left radius; the scaphoid, lunar, magnum, and unciform of the right carpus; three metacarpals of the same side, and a few phalanges. The bones are those of a single individual of a new species of the genus Protapirus, for which the name Protapirus robustus is proposed. It is considerably larger than any of the White River species of Protapirus, and would approximate in size the most specialized living tapir, Elasmognathus bairdii. The lower jaw is represented about onehalf natural size in Fig. 1. The symphysial region was found in place, imbedded in a buff colored tuff so characteristic of the Upper John Day beds that the expression "buff beds” was used as a convenient field term for this horizon. The other bones lay

loose on the surface in the immediate vicinity.

"A Contribution to the Geology of the John Day Basin," Bull. Dept. Geol., U. of Cal., Vol. II, No. 9, p. 296; JOUR. GEOL., Jan.-Feb., 1901, p. 72.

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