914 



SCIENCE. 



[N. S. Vol. XVI. No. 414. 



it has been conclusively shown to be gener- 

 ieally identical with Ophthalmosaurus or Ich- 

 thyosaurus. On the other hand, some may 

 contend that the present specimen is dis- 

 tinguishable generically from Baptanodon, 

 although the writer at present does not believe 

 this. 



Should further studies or future discoveries 

 demonstrate the present specimen to pertain 

 to a distinct genus and species, it might then 

 be very appropriately called Microdoniosauru.s 

 petersonii, and should those forms previously 

 described by Marsh still prove to be edentu- 

 lous this character would alone be sufficient 

 to distinguish it generically from Baptano- 

 don. To definitely distinguish it, however, 

 from Ophthalmosaurus is at present not pos- 

 sible, and the American and European forms 

 may yet prove to be generically identical. 



This discovery is of further importance 

 from a geological standpoint. The existence 

 of forms so similar in beds which in America 

 have been referred by Marsh and others to 

 the lower Jurassic and in England and Europe 

 to the Liassic is of the greatest value for pur- 

 poses of correlation, and if it does not dem- 

 onstrate the equivalent age of these two de- 

 posits it at least furnishes additional evidence 

 in favor of the Jurassic age of the conform- 

 ably and immediately overlying Atlantosaurus 

 beds of Marsh, as was consistently maintained 

 by that author. 



The points it is desired to emphasize in 

 this preliminary paper are: 



1. The presence of Ichthyosaurians with 

 teeth in the American Jurassic. 



2. The great similarity and perhaps generic 

 identity of Baptanodon and Ophthalmosaurus. 



3. The further evidence it affords in favor 

 of the Jurassic age of the Atlantosaurus beds 

 of Marsh, which has been seriously questioned 

 hy some authorities.. 



This material will be more fully described 

 and illustrated in a paper now in preparation 

 by the present author. 



Charles W. Gilmore. 

 Carnegie Museum, 

 November 12, 1902. 



CURRENT NOTES ON PEY8I0GRAPHT. 



RIVERS OF SOUTH DAKOTA. 



The ' Hydrographic History of South Da- 

 kota,' by J. E. Todd (Bull. Geol. Soc. Amer., 

 XIII., 1902, pp. 27-40, maps) summarizes the 

 work of some ten years in serviceable form. 

 The general eastward slope from the Eocky 

 mountains and Black hills (whether result- 

 ing from the tilting of formerly level lacus- 

 trine strata, or from the slant of fluviatile 

 deposition) determined the delivery of six 

 east-flowing streams to a preglacial geosyn- 

 clinal south-flowing trunk river whose course 

 is roughly represented by James river in 

 eastern Dakota and by the existing Missouri 

 further south. The broad James valley was 

 invaded by a great ice lobe, 1,000 to 2,000 feet 

 thick, in the latest (Wisconsin) epoch of the 

 glacial period; the east-flowing streams were 

 thereby obstructed, with the result of produ- 

 cing temporary lakes whose combined south- 

 ward outlets across the preglacial interfluves 

 determined the Missouri river in Dakota. 

 Evidence of the changes thus involved is 

 found in the abundant moraines on the pres- 

 ent divide between Missouri and James, in 

 the masked extension under these moraines 

 i.if the preglacial east-sloping valleys and 

 their interfluves, in the shore lines of various 

 temporary lakes, and in the apparently 

 younger form of the Missouri valley where 

 it cuts through the interfluves, although but 

 few details are given on the latter point. The 

 associated changes in several other rivers are 

 traced. 



ARGENTINE-CHILEAN BOUNDARY. 



A REMARKABLE report by the Argentine 

 commissioners on the Argentine-Chilean 

 boundary has been presented to the British 

 arbitration tribunal. It consists of five 

 quarto volumes, printed for the Argentine 

 government by Clowes (London, 1900), with 

 numerous photographic plates and maps, from 

 which a great amount of geographic and 

 physiographic information may be obtained. 

 The disinite that the arbitration tribunal is 

 to settle turns, as is not infrequently the case 

 in such disputes, ixpon an insufiiciency of 

 physiographic detail in the description of 



