292 proceedings: geological society 



region lies along a heavily loaded sea coast, the nature of the lateral 

 thrust is not difficult to understand. The fact that the surface beds 

 are undisturbed, except immediately around the salt plugs, is ex- 

 plained by the nature of the section — a series of indurated and rigid 

 formations overlain by a great thickness of relatively yielding and 

 plastic sediments. Indirect evidence of the origin of the plugs is also 

 afforded by their identity in structure and composition with the Euro- 

 pean salt stocks, the tectonic origin of which is declared to be unmis- 

 takable. 



The 332nd meeting of the Society was held in the Cosmos Club 

 Wednesday evening, March 12, 191 9, President Ulrich presiding and 

 46 persons present. 



informal communications 



G. W. Stose: Travertine from Rock Creek Park, District oj Columbia. 

 Travertine occurring in a granite country would seem to be unusual, 

 but travertine has recently been found on the granite and schist in 

 Rock Creek Park, near Blagden Mill road. This deposit of aragonite 

 travertine occurs at the mouth of an apparently large spring which 

 empties into Rock Creek. On investigation the spring proved to be 

 an overflow from a nearby city reservoir. It seems therefore that the 

 travertine deposit came from lime dissolved out of the cement in the 

 masonry of this reservoir and its conduit. 



In discussing Mr. Stose's paper, R. S. BasslER, of the National 

 Museum, called attention to the deposit of calcareous stalactites in a 

 culvert under the aqueduct along Potomac River in the District of 

 Columbia. These stalactites are derived from lime used in the masonry 

 of the aqueduct, and a new crop is found on each annual visit of a class 

 in geology. 



R. B. Sosman: The temperature inversions in the fumaroles of the 

 Valley of Ten Thousand Smokes, Alaska Peninsula. The peculiar 

 inversion of temperatures in the fumaroles of the Valley, which was 

 discovered in 191 8 and reported by Prof. R. F. Griggs in his lecture 

 before the Washington Academy of Sciences on February 18, 191 9, 

 and which seemed at first the most puzzling feature of the fumaroles, 

 may find explanation in the "velocity cooling" which is known to 

 occur in a jet of gas issuing from an orifice. It has been observed 

 experimentally by Joule and Thomson' and by Bradley and Hale^ in 

 high-pressure air jets, and is discussed by S. A. Moss'^ in connection with 

 experiments on steam flowing from orifices. The cooling effect is due 

 to the conversion of heat energy into translational kinetic energy, 

 which is subsequently converted back into heat when the high-velocity 

 jet of steam is checked. We have here the possibility that the ap- 

 parent temperature of a jet, as measured by a thermometer, will show 

 variations with the shape and size of the thermometer. 



' Joule and Thomson. PhiL Mag. (4) 4: 491. 1852. 



2 Bradley, W. P., and Hale, C. F. Phys. Rev. 29: 266. 1909. 



^ Moss, S. A Trans. Amer. Soc. Mech. Eng. 38: 766. 1916. 



