84 



SCIENCE. 



[N. S. Vol. VII. No. 160. 



The ratios of the molecular equivalents of 

 the alkalies to the silica were used as the 

 ordinates, by which the dot indicating the 

 particular analysis was located on the chart, 

 while the actual silica percentages were 

 employed as the abscissas. Very interest- 

 ing and suggestive groupings of rocks re- 

 sulted, and charts were shown that ex- 

 hibited in a graphic way many peculiar 

 points of composition. 



Adjournment was then had for lunch. 

 On re-assembling after lunch the following 

 papers were read : 



Concentric Weathering in Sedimentary Bocks. 



T. C. Hopkins, State College, Pa.; read 



by G. O. Smith. 



The paper was a brief explanation of four 

 photographs showing concentric structure 

 in shale and fire-clay beds in western Penn- 

 sylvania. In some places they show a 

 double concentric structure ; one on a large 

 scale, starting from the joint planes and re- 

 sembling exfoliation ; another on a smaller 

 scale, showing flattened concretions of vary- 

 ing sizes. 



New Geothermal Data from South Dakota, etc. 



N. H. Darton, "Washington, D. C; 



read by W. B. Scott. 



By means of two large scale maps of 

 South Dakota the curious variations in 

 the temperature of the water from the 

 artesian wells of the region were shown. 

 All are warm, but the temperatures differ. 

 Assuming that the temperature of the water 

 indicates the temperature of the rock 

 stratum that yields it, and using this in 

 connection with the depth of the well and 

 the mean annual temperature at the sur- 

 face, very high rates of increase in depth 

 are shown. They vary from an extreme of 

 18 feet for 1° F. west of the Missouri river 

 to 35 feet for 1° F. at the last point re- 

 corded in eastern South Dakota. Belts 

 were marked off according to the gradients 

 20-25 feet, 25-30 feet and 30-85 feet per 



degree. This developed a long, narrow 

 east and west belt of relatively low gradi- 

 ent, projecting westward into the areas of 

 higher gradient, and corresponding to the 

 nearness to the surface of one of the lower 

 geological formations. The maps are, how- 

 ever, necessary to make the relations clear. 



Note on an Area of Compressed Structure in 

 Western Indiana. George H. Ashley. 

 This paper was read by J. J. Stevenson. 

 It emphasized the great lack of any evi- 

 dences of disturbance throughout Indiana, 

 as the geology of the State presents remark- 

 able regularity of strata. Recently, how- 

 ever, the author had found near Asherville, 

 in the block coal region, a great number of 

 small faults, some even reversed, and cited 

 them as evidence of local compression. 



Niagara Gorge and St. David's Channel. 



Warren Upham, St. Paul, Minn.; read 



by T. C. Chamberlin. 



Having recently again examined the 

 Niagara falls and gorge, with especial ref- 

 erence to the older channel of St. David's, 

 the author believes that a most important 

 element in the history of the gorge erosion 

 has been overlooked by some observers, 

 and that by others its evidences have been 

 misunderstood. This paper shows that the 

 small preglacial stream which eroded the 

 St. David's and Whirlpool channels, having 

 a great depth beneath the river in the 

 Whirlpool, must have flowed for a consider- 

 able distance, before reaching that depth, 

 in a gradually widening and deepening 

 ravine, coinciding with the present gorge 

 along the Whirlpool rapids. Because the 

 Niagara River found there a drift-filled 

 narrow ravine, which is cut to the present 

 size of the gorge, its erosion took place in 

 that part by rapids and cascades. South- 

 ward from the head of the old ravine the 

 river has eroded its gorge by a great verti- 

 cal cataract, under which the masses of the 

 Niagara limestone, rolled about by the 



