Febeuaky 8, 1907] 



SCIENCE 



229 



clusively demonstrated by comparing Tables 

 I. and II. The first of these tables shows, 

 with only two exceptions, namely, at noon 

 and 4 p.m. December 22, that at the time when 

 the observations were made there was an in- 

 going current. Table II., which gives the 

 barometrical readings, shows that the time of 

 recorded ingoing currents, except at noon, 

 December 24, was during the time of increas- 

 ing atmospheric pressure ; and that in the two 

 exceptional cases, which showed outgoing or 

 no currents, the atmospheric pressure was de- 

 creasing. In other words, the outgoing cur- 

 rents always take place during rising barome- 

 ter, and ingoing currents during falling 

 barometer. As the atmospheric pressure 

 usually increases daily from 4 a.m. to 10 a.m. 

 and decreases from 10 a.m. to 4 p.m., it follows 

 that springs, wells and caves of this class will 

 generally have an indraft in the forenoon and 

 an outdraft in the afternoon. If the daily 

 variations of atmospheric pressure were regu- 

 lar, the ingoing and outgoing currents would 

 also be regular and would take place at the 

 same time each day. However, as the daily 

 maximum and minimuiu barometric readings 

 may vary greatly from day to day, due to 

 approaching storms or other causes, the ingo- 

 ing and outgoing currents will not always act 

 with the same energy. 



In the second class of wells and springs, the 

 constantly outgoing or the constantly ingo- 

 ing current is entirely independent of atmos- 

 pheric conditions. The currents, whether 

 outward or inward, act with equal energy 

 during high or low barometer and always move 

 in the same direction. The Boston and the 

 Lester deep wells are excellent examples of 

 wells and springs of this class. The phe- 

 nomenon which they exhibit seems to be due 

 entirely to the friction of the air on a rapidly 

 moving current of water. This phenomenon 

 is beautifully illustrated in Richard's water 

 air-blast, to be found in many well-equipped 

 chemical laboratories. In the Boston well, and 

 also in the Lester well, appear almost exactly 

 the same conditions met with in Richard's 

 water air blast. The well itself forms the 

 inlet for the air, and the rapidly flowing 

 stream in the subterranean channel below 



completes the conditions necessary for an in- 

 going air blast. As the air in the wells here 

 named is constantly drawn in, it naturally 

 follows that it must escape at some other 

 point as an outgoing current, thus giving rise 

 to continuously blowing caves or springs. 



As underground streams frequently pass 

 from one bed of rock to another in their sub- 

 terranean course, they, no doubt, often form 

 waterfalls which possess all the essential con- 

 ditions necessary for producing an air blast, 

 thus giving rise to continuously blowing 

 caves and springs. 



S. W. McCallie 



Georgia School of Technology 



CURRENT NOTES ON LAND FORMS 



GLACIATION OF THE BIG HORN MOUNTAINS, 

 WYOMING 



A RECENT report on the ' Geology of the 

 Big Horn mountains ' by N. H. Darton (Prof. 

 Paper 51, U. S. Geol. Surv., 1906; excellent 

 plates) describes the range as a wide anticline 

 with steeper dips on the east, eroded suf- 

 ficiently to expose its granitic core over the 

 broad arching crest, while scalloped ridges of 

 the more resistant members lie along the 

 flanks and in places stretch over toward the 

 axis of the range. R. D. Salisbury presents 

 a chapter on glaciation — in which there is to 

 our view an insufficient recognition of the 

 previous work of F. E. Matthes on the same 

 district — showing that many glaciers occupied 

 the upper valleys during the last glacial epoch. 

 Erosion by these glaciers, working in valleys 

 that had been previously developed by normal 

 preglacial erosion, is held responsible for ' the 

 development of cirques, the cleaning out of 

 the upper parts of the valleys through which 

 the ice passed, the rounding and widening of 

 the valley bottoms, the polishing of the rock 

 surfaces in the valleys and the excavation of 

 some of the lake basins.' The cirques head 

 in superb cliffs, which rise abruptly to the 

 broad highland surface of the unglaciated 

 granite; sharply serrate ridges occur where 

 the widening of neighboring cirques and 

 troughs has consumed the intervening high- 

 land surface; here the mountains gain a dis- 



