Mathematical Question, 233 



to the Geological Society, to which I shall answer as briefly as 

 possible. The muscle "shells found in the shale of this part of 

 the kingdom are mineralized by clay iron stone, and exactlv re- 

 semble the common fresh-water muscle in shape, but are less ia 

 size. I beg leave further to add, that no organic remains which 

 I could suspect to have once belonged to marine animals, were 

 ever observed by me in the Newcastle coal formation, Inough 

 the niagnesian limestone by v/hich it is covered, and the lead 

 mine sills lying below it, "abound with tliem. With regard to 

 the grindstone sill on Alston Moor, it consists of a sandstone not 

 unlike the stratuni from which grindstones are quarried in tliis 

 vicinity, but the former must be situated far below the latter. 

 As Mr'. W. Forster's section is referred to in the letter of my ano- 

 nymous correspondent, permit me to say, that in the year 1800 

 a similar engraving was published at Carlisle (and signed fVittiam 

 Millot, muicr), of all the lead mine measures; and previous to 

 that period the late Mr. G. Johnson had an engraving made of 

 the strata sunk through at the coal mine situated at Byker St. 

 Anthony. These two, together with the section of Sheriff-hili 

 Collierv, printed in Hutchinson's History of Durham, furnish 

 out the section given to the public by Mr. Forster in 1812. 

 MSS. of all these documents have been in the library of the Li- 

 terarv and Philosophical Society of this place for twenty years 

 past. For the directions and description of the lead veins, which 

 are certainly highly valuable in a geological point of view, the 

 world are indebted to Mr. Forster. 



Your obedient servant. 

 To the Editor of Nat. John Winch, 



The Phil. Mag. and Journal. 



MATHEMATICAL QUESTION. 



Plviiiouth, March 11, 1815. 

 Sir,— I HAVE been long baffled in my attempts to integrate 



'S 

 t!ie following differential, viz. — t Tj which occurs m 



a very interesting department of Hydrodynamics, at art. ccccliv. 

 page'418, of Dr. Gregory's excellent Treatise of Mechanics. 

 It is possible that some of your learned correspondents may be 

 able to accomplish the integration, and you will therefore much 

 pblige me by inserting this in your next number. 



Yours, &c. 

 To the Editor of George Harvey. 



The Phil. Mag. and Journal. 



*,* Our limits oblige us to entreat any of our correspondents who may 

 jinbwer Mr. llurvey, to be as brief as posiible. 



Ol'llCS. 



