Geological Society. 229 



variation which then remains exhibits a very decided double period 

 in this direction also. These variations with double periods are re- 

 garded as indicative of the existence of a double diurnal variation 

 in the general movements of the atmosphere. Upon this hypo- 

 thesis typical diurnal variations of the wind are deduced for north 

 and south low latitudes — that for north latitudes exhibiting a 

 double diurnal right-handed rotation, and that for south latitudes 

 a double diurnal left-handed rotation ; and from these the diurnal 

 variation of the barometer is deduced. 



The movements of the wind- vane at Bombay are then analyzed ; 

 and the writer concludes that the greater part of the excess of 

 " direct " over " retrograde " rotation of the vane at Bombay is due 

 to the diurnal variation of the wind. 



Extracts are given from observations made at St. Helena, To- 

 ronto, and Falmouth, showing the character of the diurnal wind- 

 variations at those places, and their greater or less agreement 

 with the deduced typical curves. The writer maintains that these 

 variations afford independently a possible, if not a probable, ex- 

 planation of that movement of the air which Dove had called the 

 "Law of Gyration;" and, in conclusion, he points to the extent 

 of their applicability in deducing weather probabilities, and to the 

 method of discussing storms. 



A postscript is added, giving the mean diurnal variation of the 

 wind at Sandwick Manse, Orkney, and pointing out its general 

 conformity with the results deduced from the Bombay wind-obser- 

 vations. 



GEOLOGICAL SOCIETY. 



[Continued from p. 77 .] 



February 26, 1873.— Prof. Ramsay, F.R.S., Vice-President, 



in the Chair. 



The following communications were read : — 



1. "On the Jurassic Pocks of Skye and Raasay." By James 

 Bryce, M.A., LL.D., F.G.S. 



In this paper the author described numerous sections of Jurassic 

 rocks exposed chiefly in the sea-cliffs of Skye and Raasay, indicating 

 the presence in those islands of a complete series of beds ascending 

 from the Lower Lias to the middle of the Middle Oolite. He 

 noticed the occurrence in these sections of fossils belonging to the 

 zones of Ammonites angulatus and A. BucJclandi in the Lower Lias, 

 to the zones of A. Jamesoni, A. capricornus, A. margaritatus, and 

 A. spinatus in the Middle Lias, of Upper Lias fossils, including 

 Ammonites communis, falcifer, JieterophyUus, and bifrons, and of 

 others indicating beds belonging to the Inferior Oolite and Corn- 

 brash and to the Oxford Clay. The Loch-Staffm beds were described 

 as an estuarine series, nearly approaching the Oxford Clay in geo- 

 logical age, and including a bed almost entirely made up of the 

 shells of Ostrea kebridica. 



The whole series of Jurassic rocks in these islands reposes on the 

 Torridon sandstone of Cambrian age ; and the author discussed the 



