418 



SCIENCE. 



[N. S. Vol. III. No. 63. 



body, the remainder of the omatidium with its 

 refractive cone and retinula is practically iden- 

 tical with the omatidium of Gammarus, minus, 

 of course, the corneal cuticula. For in the re- 

 tinula of both crustaceans there are five retinal 

 cells with pigment, and four rhabdomeres. 

 There are two of these peculiar crater-like 

 eyes that project from either side of the cepha- 

 lon of Byblis serrata. 



Vernon Bailey exhibited Two Mammals New 

 to the Vieinity of Washington, being Sorex per- 

 sonatus and Synaptomys Cooperi. In 1888 skulls 

 of these mammals were found in pellets ejected 

 by the Long-eared Owl, but until the capture 

 of the specimens shown, which were taken at 

 Hyattsville it had not been definitely proved 

 that these species were found in the immediate 

 vicinity. F. A. Lucas, 



Secretary. 



GEOLOGICAL SOCIETY OF WASHINGTON. 



At the meeting of the Geological Society of 

 Washington (D. C), held on February 26, 1896, 

 the following communications were presented: 



Mr. W J McGee exhibited the geologic map 

 of the State of New York recently printed by 

 the United States Geological Survey in coopera- 

 tion with Prof. Hall, State Geologist. He 

 stated that the map had been in preparation 

 for the last ten years and its preliminary draft 

 was a compilation by Prof. Hall and himself in 

 greater part from old data. Finding that these 

 were very incomplete and unsatisfactory in 

 many areas, new field work was begun and 

 continued for several years. In the meanwhile 

 a new base was compiled from county maps and 

 other sources. The larger part of the field 

 work was done by Mr. N. H. Darton, of the 

 United States Geological Survey, who mapped 

 the geology of nearly the entire area of the 

 Helderberg and associated formations, the 

 faulted area extending along the Mohawk valley 

 and around the southern side of the Adiron- 

 dacks to Lake George, the Niagara escarpment, 

 the northern and eastern portions of the Cats- 

 kill Mountains, the Oneonta region, the greater 

 portions of Albany, Ulster, Orange and Rock- 

 land counties, and the Juratrias area of New 

 Jersey. Dr. F. J. H. Merrill contributed data 

 for Westchester, Putnam and New York coun- 



ties, and Prof. J. F. Kemp mapped much of 

 the region lying along the eastern side of the 

 Adirondacks. Data for smaller areas were ob- 

 tained from published or manuscript maps by 

 Messrs. C. D. Walcott, T. N. Dale, J. H. 

 Clarke, W. M. Davis, W. B. Dwight, Mr. Ran- 

 dall, Prof. Smythe and others. The map was 

 edited by Mr. Willis Bailey. 



Notes on the Geology of the Black Hills of 

 Dakota were presented by Mr. N. H. Darton. 

 The region was visited last autumn for a study 

 of the outcrops of the Dakota sandstones and 

 the associated formations, in connection with an 

 investigation for the United States Geological 

 Survey of the artesian waters of the Dakotas. 

 There was first described a detailed section 

 which had been carefully measured from the 

 base of the Potsdam to the White River Miocene 

 formation, along a line passing through Rapid 

 City to the Bad Lands. The thickness of the 

 upper Cretaceous members in this section have 

 since been most satisfactorily verified by the 

 deep well-boring on the Rosebud Indian Reser- 

 vation. The salient features of the general 

 stratigraphy were pointed out and the alleged 

 unconformities in the Juratrias formations were 

 discussed. Attention was called to a well- 

 defined peneplain now represented by the east- 

 ern ' hog back ' foothills of which the very even 

 crest lines are at an altitude very nearly 4,000 

 feet above sea level for over 100 miles. Dia- 

 grams were exhibited of a very interesting 

 laccolite west of Tilford, and the structure of 

 the Bear Butte and Warren Peaks eruptive 

 areas were described. Some incidental obser- 

 vations in the nucleal region of the hills brought 

 to light some important details of stratigraphy 

 of the Algonkian beds, and some examples 

 illustrating the development of schistosity in 

 the vicinitj' both of granite and younger erup- 

 tives. 



Several miscellaneous specimens were shown, 

 including cone-in-cone structure developed in 

 Pierre clays by the pressure caused by the for- 

 mation of sideritic concretions ; material from 

 sandstone disks in the Bad Lands, having verti- 

 cal cleavage into thin plates with horizontally 

 corrugated surfaces, and masses of phosphated 

 gi'ains from the Pierre clays, which appear to 

 be of coprolitic character. 



