Intelligence and Miscellaneous Articles. 319 



troughs and winding hollows which form the beds of the streams, 

 the rocks on the higher ground being either bare or hidden by a 

 growth of peat and heather. It thins out at altitudes of from 100 

 to 150 feet, and its thickness is therefore very variable, though it 

 seldom much exceeds 100 feet. Mr. Jamieson first described the 

 distribution of the drift-beds over the area in question, their texture 

 and colour at the different localities where they occur, and the 

 nature and appearance of the stones and boulders found in them ; 

 he then noticed the broken state of the shells, the most common 

 species being Cyprina Islandica, Astarte borealis, A. elliptica, Tellina 

 calcarea, T. Balthica, and Turrit ella ungulina. The direction of the 

 glacial markings on the rocks was shown to be pretty uniformly 

 from N.W. to S.E. (true) ; so that it must have been produced by a 

 movement of ice proceeding from an external region to the N.W., 

 and not by glacier-action proceeding from the interior of the country, 

 as is the case in the midland region of Scotland. The glacial drift 

 of Caithness and the old boulder-clay of the middle of Scotland 

 resemble one another in their physical arrangement, but differ in the 

 prevalence of marine organisms in the former. The absence of tran- 

 quilly deposited glacial-marine beds, of moraines, and of gravel 

 hillocks, and the deficiency of valley-gravel in Caithness, are also 

 points in which the glacial series of that area differs from that of 

 Central Scotland ; and Mr. Jamieson inferred that, of the two series, 

 the Caithness drift was the more recent. In conclusion the author 

 described the deposits of the Postglacial period in Caithness, and 

 showed that they did not differ materially from those occurring in 

 the rest of Scotland. 



XL VI II. Intelligence and Miscellaneous Articles. 



ELECTRICAL CONDUCTIVITY OF GASES UNDER FEEBLE PRESSURES. 

 BY A, MORREN. 



PJiHE author alludes to the experiments which M. A. de la Rive 

 -*- made on the conductivity of nitrogen and hydrogen ; and he pub- 

 lishes the results at which he himself has arrived either with these 

 gases or with others. 



The author enters into details on the subject of the methods which 

 he used in his experiments. It is sufficient to mention that, in rare- 

 fying the gases, he used a mercury aspirator provided with two ma- 

 nometers, one a mercurial one, the other containing sulphuric acid, 

 so that the pressure on the gas could easily be determined to one- 

 tenth of a millimetre of mercury. 



The electricity was furnished by a Ruhmkorff 's coil put in action 

 by four Bunsen's elements ; and the intensity of the current was mea- 

 sured by a galvanometer formed of copper wire, 25 metres in length 

 and one-tenth of a millimetre in diameter. The gas is slowly rarefied, 

 so as to catch the moment of the first deflection ; and at each instant 

 the elastic force of the gas, and the corresponding deflection of the 

 galvanometer, were accurately noted. To compare with greater cer- 

 tainty the results obtained with various gases, the author had to 



