Intelligence and Miscellaneous Articles. 475 



Part of the sands at Bradford Abbas really represent the lower- 

 oolitic mass of Leckhampton and Crickley ; in fact the Dorset sands 

 represent the lower freestones of Gloucestershire. The beds under- 

 lying the Dorsetshire Cephalopoda-bed are the equivalents of the 

 Inferior Oolite of Ham Hill. 



The author gives lists of the fossils from the freestone of Ham 

 Hill, and of the Cephalopoda from the Dorset equivalent of the 

 " Gryphite Grit." The latter do not appear in zones ; but dif- 

 ferent species are prevalent at different localities, all on the same 

 horizon. The other fossils from this bed point to the same con- 

 clusions, as the Ammonites are numerous and in good preservation. 



24. " Evidence of the Subsidence of the Island of Guernsey." 

 By E. A. Peacock, Esq., C.E., E.G.S. 



All round the coast of this island, like that of Jersey, are found 

 tree-trunks and other vestiges of old forest-land now submerged. Pas- 

 sages are quoted by the author from various old historians relative 

 to the former existence of this tract as dry land, the submergence of 

 which probably took place in the fifteenth century. The encroach- 

 ment of the waters is due to the subsidence of the land, and not, as 

 has been suggested, to the breaking in of the sea through some 

 natural barrier upon some already low~-lying district. Judging 

 from the old chart of 1406, the amount of depression is equal to 

 160 feet. 



LIX. Intelligence and Miscellaneous Articles. 



ON THE EOTATOEY POLARIZATION OF QUARTZ. 

 BY J. L. SORET AND ED. SARASIN. 



TN a former memoir on the rotatory polarization of quartz*, we 

 -*- announced the intention of extending our observations to the ul- 

 tra-violet rays more refrangible than the line N, and of giving at the 

 same time to our measurements a higher degree of precision. It 

 is the results of these fresh researches that we have now the honour 

 of communicating to the Academy. 



To determine the angle through which quartz rotates the plane 

 of polarization of rays of various wave-lengths we have, as before, 

 operated upon solar light by the method of MM. Eizeau and Fou- 

 cault. The left-handed quartz crystal w T hich we have chiefly made 

 use of has been retouched in its cutting so as to render its faces 

 perfectly parallel, and perpendicular to the crystallographic axis. 

 Its thickness is 29*885 millims. We have carefully determined 

 its temperature for each measurement, and corrected the obtained 

 values of the angle of rotation by reducing them, with the aid of 

 the formula given by Yon Lang, to the temperature of 20°. 



* Comptes Rendus de VAcademie des Sciences, Oct. 11, 1874, t. lxxxi. 

 p. 610; Phil. Mag. [4] vol. 1. p. 492. 



