144 



SCmNGE. 



[N. S. Vol, XI. No. 265. 



TBETIAEY SHORE LINES AND DEPOSITS IN THE 

 BLACK HILLS. 



N. H. Darton, U. S. Geol. Survey. 



It has been found that the ' White River ' 

 (01igoc8ne),lake deposits of western South 

 Dakota extend far up the flanks of the 

 Black Hills to shore lines, which are beau- 

 tifully exhibited in a portion of the region. 

 The relations of these deposits throw im- 

 portant light on the physiographic develop- 

 ment of the uplift at several of its stages. 



The paper was beautifully illustrated by 

 lantern slides, but as the hour was late and 

 no discussion ensued. 



In the evening the Society attended the 

 reception and session of the Washington 

 Academy of Sciences, at which Messrs. 

 Merriam, Gannett, Gilbert and Dall de- 

 scribed its general results. A collation fol- 

 lowed, which afforded an admirable and 

 welcome opportunity for social intercourse. 



The last session of the meeting was called 

 to order at 9:45 A. M., on Saturday, De- 

 cember 30th, and showed a rather slim at- 

 tendance owing to the departure of many 

 of the members. 



The first paper was presented by G. O. 

 Smith and W. C. Mendenhall, and was 

 on the ' Tertiary Granite of the Northern 

 Cascades, Washington.' This granite, which 

 a later petrographical study may show to be 

 a quartz monzonite or quartz diorite, extends 

 over an area of at least 100 square miles. It 

 is intrusive between the Tertiary sedimen- 

 taries, as shown by the numerous dikes 

 penetrating the surrounding rocks. The 

 sedimentary rocks are slates, sandstones 

 and conglomerates, and show interesting 

 contact phenomena. Much of the slate is 

 metamorphosed into hornfels, and there is 

 abundant development of such minerals as 

 garnet, epidote and tourmaline along the 

 contacts. 



This intrusive mass is important in its 

 relation to the age of the sedimentaries, and 



also in its relation to the basaltic flows 

 farther south. 



Professor W.M. Davis read the next paper 

 on ' The Basin Deposits of the Eocky 

 Mountain Region.' 



The writer questioned the origin of the 

 Tertiary lake beds of the West, and cited 

 examples to prove his theory that many of 

 them are fl uviatile in origin . The sorting out 

 and distribution of the sediments compris- 

 ing the strata in these beds indicated stream 

 deposition, and, therefore, basin deposits, 

 rather than lake deposits, is the proper 

 term for these beds. He classed deposits 

 according to three modes of origin — •' la- 

 custrine,' 'fluviatile' and 'wash,' and 

 argued for the fluviatile and occasionally 

 the ' wash ' origin of many of the so-called 

 ' Tertiary lake beds ' of the Rocky Moun- 

 tains. His theory was opposed by Messrs. 

 Weed, Emmons, Cross and Russell, all of 

 whom upheld the lacustrine origin of most 

 of these deposits. 



Professor A. P. Coleman presented a short 

 paper on ' Heronite and its Related Rocks.' 



Professor Coleman exhibited some speci- 

 mens of this new analcite rock, which 

 occurs as a series of parallel dikes near 

 Heron Bay, Lake Superior. The rock cor- 

 responds chemically to nepheline syenite, 

 and he thought perhaps a petrographical 

 study would show the presence of nephe- 

 line. The typical rock consists of analcite 

 in which radiating bundles of feldspar and 

 acgirine crystals are imbedded : while a 

 variety occurs with more feldspar in fluidal 

 arrangement, and a second variety where 

 the feldspar is in the form of spheres, some- 

 times two inches in diameter. 



The succeeding paper was by Dr. H. S. 

 Washington on the ' Magnet Cove Lacco- 

 lith.' Since the excellent work of the late 

 Dr. J. Francis Williams on the Igneous 

 Rocks of Arkansas, much more has become 

 known through the work of Brogger, La- 

 gorio and others about magmatic differentia- 



