184 Rev. J. J. Conybeare on the [March, 



the commanders, miss the harbour altogether, the loss in conse- 

 quence is not chargeable upon the entrance. 



Entrances that face the calmest quarter, and that do not 

 receive the surf, are at 

 right angles, or nearly so, 

 to the main shore. Let 

 A, fig. 2, be such an en- 

 trance to the harboui B, 

 facing the high shore o s ; 

 a b is the main pier, and 

 n m the inner pier. The 

 exterior lines of approach, 

 e b, c b, are obtained by 

 allowing such space in 

 front of the shore a t, i 1:, 

 and g h, as will keep ships 



sailing on these lines from rocks and shallow water ; and if they 

 have within them 146° 15', then a vessel can reach the pier- 

 head b in any wind. But as the side c is open in strong sea 

 gales, vessels are some times carried too far past the head b to 

 turn into the harbour-mouth A ; and the same happens in gales 

 out of the harbour-mouth A : vessels so driven aside are forced 

 upon the contiguous rocks or sandy shore, and are destroyed or 

 much injured. So it has happened after an entrance of this 

 kind has been tried to a large harbour, and where money could 

 be obtained, that outworks have been erected on the exposed 

 side c, which assimilate the principle of this entrance, when so 

 modified, very closely with that of the first kind of entrance. 



I am, Sir, yours, &c. 



J. B. Longmire. 



Article V. 



On the Geology of Devon and Cornwall. 

 By the Rev. J. J. Conybeare, MGS. 



(To the Editor of the Annals of Philosophy.) 



MY DEAR SIR, BathEaston, Feb. 2, 1823. 



The notice of such geological travellers as first visited Corn- 

 wall and Devonshire was of course most strongly attracted by 

 those which may be termed their metalliferous districts, and 

 these still do and must always continue to present the most 

 immediate and interesting objects of such research. Soon also 

 the attention was directed to such points of the coast as are 



