392 Geological Society: — 



by integration ; its importance arises from the fact that it serves 

 to express the work done by the forces which are found to be 

 actually exerted in Nature. In the second part of the work Pro- 

 fessor Clausius states with great clearness the various steps by 

 which the Potential is at length arrived at. Thus, beginning with 

 a very careful statement of the principle of Virtual Velocities, he 

 passes on through D'Alembert's principle to the proposition of the 

 Equivalence of Vis Viva and work, and thus arrives at the notion 

 of the " ergal," i. e. the function (Q,), if such a function exists, 

 given by the equation 



2(Xdx + Ydy + Zdz) = —dQ,. 

 He then discusses two cases in which the forces of a system in 

 motion have an " ergal," and finally arrives at the potential by a 

 limitation exactly resembling that by which the potential function 

 is obtained from the force-function. 



LV. Proceedings of Learned Societies. 



GEOLOGICAL SOCIETY. 

 [Continued from p. 316.] 



February 20, 1878.— Henry Clifton Sorby, Esq,, E.K.S., 

 President, in the Chair. 

 npHE following communications were read : — 

 -*- 1. " Notes on the Physical Geology of the "Upper Punjab." By 

 A. B. Wynne, Esq., E.G.S. 



The author stated that crystalline rocks are rare in the accession 

 parts of the Upper Punjab district, and that when present they con- 

 sist of syenite and gneiss. The Cambrian and Silurian formations 

 are represented by more or less metamorphosed azoic slates in the 

 Himalayan district, and in the Salt range by a zone less than 200 

 feet thick, containing either Obolus or JSiphonotreta, underlain by a 

 thick unfossiliferous sandstone, beneath which is a deposit of gypseous 

 marl and salt. Above the Silurian in the Salt range, and conform- 

 able to it, comes the Magnesian Sandstone group and a group of un- 

 fossiliferous sandstones and clays ; in the Himalaya these deposits 

 are probably represented by an unfossiliferous siliceous dolomite, 

 which rests unconformably upon the slates. There are no fossils 

 indicative of rocks of Devonian age. The Carboniferous rocks 

 are also conformably deposited on limestones, sandstones, and shales, 

 the last sometimes carbonaceous. These deposits contain haematite 

 in pockets ; and the oldest known Ammonites have been found in 

 them. An infra-Triassic group occurring in Lei Bau mountain con- 

 sists of red shales, sandstones, and red quartzitic dolomites, overlain 

 by lighter-coloured siliceous dolomites, which in their turn are co- 

 vered by haematite, quartz breccia, sandstones, and shales. The 

 author believes these to have been deposited by the same waters 

 which subsequently laid down the Trias, which is largely composed 

 of limestones in the northern Himalayan area, and here and else- 

 where includes dolomites, shales, and sandstones. Numerous fos- 



