494 ^^w Variety of argillaceous Iron-ore. 



maintain its velocity. One of the principal, and moft frequent, caufes of retardation in a 

 river, is alfo produced by the eddies, which ' are inceflantly formed in the dilatations of the 

 bed, the cavities of the bottom, the inequalities of the banks, the flexures or windings of its 

 courfe, the currents which crofs each other, and the flreams which ftrike each other with 

 different velocities. A confiderable part of the force of the current is thus employed to re- 

 iftore an equilibrium of motion, which that current itfelf does continually derange. 



(To be continued.) 



_^ 



No. IV. 



■'Concerning a new Variety of argillaceous Iron-ore. By Samvel L. MlTCHlLL, M.D. of 



New York. 

 SIR, 



JL HE annexed defcription of a mineral fubftance, and the remarks upon it, are taken, by 

 permiffion, from Dr. Mitchill's manufcripts. As the fubje£i; appears to me worthy to be 

 made known to the mineralogills of Europe, I have forwarded you a copy for publication, in 

 your ufeful and inftrudive Journal ; I have the fatisfa£tion to inform you at the fame time, 

 that Mr. Bruce, a young gentleman who goes paflenger to London in the fame fhip which 

 ■conveys this note, is in poffeffion of a fpecimen of this reiaarkable foflil. 



I am. Sir, 



Your very obedient fervant, ■ 

 Neiv-Tork, November x-j, 1798. ADOLPH. C. LENT, M.D. 



To Mr. W. Nicholfon. 



ut new Variety of Iron-ore of the argillaceous E^ind, and figured fomewhat Hie Bafaltes. 



The fpecimen of cohimnar iron-ore in my colleftion is from Germany, and correfponds 

 very well with Mr. Kirwan's fecond variety of his firfl; family of argillaceous iron-ores- 

 (a. Elements of Mineralogy, Dublin, 1 796.) I knew of no other iron-ore of that charafter, 

 until a few months ago. As I was walking on my farm upon Long-ifiand, furveying the 

 various mineral produ£lions that lay thick under my feet, I obfcrved a fmail fpot, that ap- 

 peared to be paved, with ftones of a regular figure ; on taking up fonie of them and exa;j)ining 

 them, they were evidently of the fame conftitution with the common argillaceous iron-ftone, 

 which lay fcattered about in rude lumps. They were, however, of a fingular Ihape. They 

 were about four inches long ; and ftood erect, fide by fide of each other, in a iliff loam. Each 

 of them had five fides and five angles ^ and though not exaiSt pentagons, were readily dif- 

 tinguilhable in moft of the fpecimens from one end to the other. This fhape was moft 

 perfeft at the two ends, which were confiderably larger than the middle part, and about one 

 inch and a half acrofs. So that when a fpecimen of this ore was grafped in the hand, it had 

 ibme refemblance of a double-headed peftle. In fome, however, four fides only were to be 

 traced. 



The 



