Correspondence, 525 



ON THE OCCURRENCE OF MOLYBDENITE IN LEICESTERSHIRE 

 AND OF LINARITE IN CORNWALL. 

 To the Editor of the Geological Magazine. 

 SiK, — During the late meeting of the British Association I hap- 

 pened to form one of the party which visited the Mount Sorrel 

 Syenite (or granite) quarries. Some of the workmen brought us 

 specimens of what they called lead on the stone. I bought a piece 

 from one of the men, recognising in their lead the mineral Molybde- 

 nite, and since my return from Nottingham I have confirmed my 

 opinion by the ordinary tests for Molybdenum. 



I ara not aware that the occurrence of Molybdenite at Mount 

 Sorrel has been noticed hitherto ; at all events, it is not mentioned 

 either in Phillips' " Mineralogy " or in Bristow's " Glossary " as 

 occurring there. 



It will, perhaps, not be uninteresting to some of your readers to 

 learn that the mineral Linarite has been found in Cornwall. I lately 

 found a specimen at Huel Penrose, near this town, — ^a mine long 

 noted for its beautiful specimens of Pyromorphite, Mimetesite, and 

 Cerusite, and where Anglesite also occurs in small quantities. 

 I remain, Sir, your obedient servant, 



Clement D. Neve Fosteb. 

 Helston, Cornwall, 



17th October, 1866. 



SIR J. F. W. HERSCHEL ON TIDAL CURRENTS. 

 To the Editor of the Geological Magazine. 



Sir, — As it might be too much to expect you (considering the 

 great increase in the number of your contributors) for several 

 months to come, to find room for a full reply to Mr. Maw's elaborate 

 article,^ I shall at present only direct the attention of your readers to 

 what Sir J. F. W. Herschel says relative to the concentrated force of 

 tidal currents in inlets, channels, and shallow seas ; and to the great 

 variety of effects which must result from the localization of currents 

 by which they are made to assume the form of curving, eddying, 

 revolving, re-acting, returning, connecting, bifurcating, joining, de- 

 flected, and reflected streams. In speaking of "the peculiar nature 

 of the tidal undulation," the above great dynamical authority remarks : 

 " The fiiU effect of this power is only to be appreciated when we 

 contemplate the rounded foims of hills, and the branching and 

 sinuous valleys of a very large proj^ortion of the surface of the land, 

 where the action of the existing rivers, or any conceivable amount 

 of atmospheric precipitation, is quite inadequate to have performed 

 the work of excavation."^ Sir Charles Lyell and Sir Eoderick I. 

 Murchison have likewise borne testimony to the denuding influence 

 of marine currents. 



D. Mackintosh. 



Weston-Super-Make. 



1 Geol. Mag., Oct. 1866. 2 "Physical Geography," p. 91. 



