86 



SCIENCE. 



[N. S. Vol. XV. No. 368. 



The characteristic ridges on the older lava 

 streams are due to basal compression of 

 folds on the surface of the stream, these 

 folds sometimes being hollow at the top, 

 though compressed below. Lantern views 

 and specimens illustrated these features. 

 Along cracks in the lava streams, parasitic 

 cones are built up and these and numerous 

 other characters of the lava stream were 

 illustrated by lantern views. Where the 

 lava stream has come in contact with a 

 body of water, the base of the sheet ex- 

 pands and becomes cellular, although the 

 character of the lava is glassy from rapid 

 cooling. The sand of the lake or river bot- 

 toms into which the lava stream entered is 

 often cemented into the base of the sheet, 

 and gives it a white color. 



The canyon of Snake river owes its 

 peculiarities to many of the features dis- 

 cussed. Shoshone falls are due to a cone 

 or mass of hard rhyolite beneath the 

 basalt, discovered by the river. Heavy 

 lava sheets overlie the finely stratified, un- 

 consolidated lake beds exposed in the 

 canyon, which are scarcely altered by the 

 lava. The base of the latter is glassy, with 

 a few steam holes, but at a short distance 

 above, the sheet has its normal granular 

 character. From beneath the lava stream 

 or from a porous layer, numerous powerful 

 springs issue along the side of the canyon 

 below Shoshone falls. These may be called 

 ' canyon springs, ' a new term introduced 

 in the classification of springs. In the 

 northern wall of the canyon occur remark- 

 able spring-formed alcoves or side canyons, 

 which -widen out amphitheater-like, and 

 have no stream at their head. Powerful 

 springs, issuing from the fine lacustrine 

 beds underlying the lava, undermine the 

 latter and cause recession of the walls. 

 Numerous lantern views were used in illus- 

 tration of the paper. 



Professor Emerson discussed the origin 

 of these lava beds and their surface char- 



acters. He pointed out the similarity of 

 many features of these lavas to those of the 

 Hawaiian volcanoes. He compared the 

 base of the Snake river lava, resting on fine 

 lake beds, with that of the Triassic trap of 

 the Connecticut Valley, resting on the 

 Triassic sands. 



Professor Wolff discussed the age of the 

 lava flows and cones. 



Structure of the Front Range, Northern 



Rocky Mountains, Montana: Bailey 



Willis, Washington, D. C. 



The Front Range of the northern 

 Rockies consists of a series of limestones, 

 quartzites and silicious argillites somewhat 

 exceeding 9,000 feet in thickness, and 

 gently flexed in a synclinal form. The 

 wddth of the range is approximately twenty 

 miles from foothill to foothill, and the 

 synclinal structure has practically a cor- 

 responding extent. The trend of the range 

 is from northwest to southeast, and the 

 strike of the rocks is essentially parallel to 

 it. The mass is, however, not exactly 

 symmetrical in cross section, the rocks out- 

 cropping on the northeastern side compris- 

 ing probably 3,000 feet of strata lower in 

 the series than the lowest on the western 

 side. 



Approached from the east, the margin 

 of this synclinal mass is found to rest dis- 

 cordantly upon black clays and sand- 

 stones. These strata appear at some little 

 distance from the range in the Great 

 Plains, dipping deeply southwestward, but 

 where they pass beneath the great lime- 

 stone and quartzite series they correspond 

 very nearly in attitude with the overlying 

 rocks. The relation of the overlying to the 

 underlying series is, however, that of an 

 overthrust mass. In many places the black 

 shales and sandstones were found to con- 

 tain Inoceramus and Ostrea characteristic 

 of the Cretaceous. In the overlying rocks 

 Mr. Weller fortunately found fragments of 



