116 Oull'tr.es of the Mineralogy of the Ochil Hills. [Fkb. 



This I state on the authority of Mr. Giesecke, a gentleman who 

 has explored more of Europe, with a view to mineralogy, than 

 perhaps any other individual. I am, Sir, 



Your obedient humble servant, 



Charlotte-square, Edinburghy ThOMAS AlLAW. 



Ntv. 25, 1813. 



P.S. I had almost forgot the Plymouth Periwinkle, with which 

 you have been so nearly deceived. Give me leave to assure you, 

 that although you were not so fortunate as to find shells imbedded 

 in the limestone of that place, my faith in the accuracy of Mr. 

 Playfair's observation is not in the slightest degree shaken. But 

 whether you found organic remains there or not, is of little im- 

 portance ; when we find shells in the slate itself, it is of no conse- 

 quence whether they occur in the limestone that accompanies it or 

 not.* 



Besides the situations in which I found shells in grauwacke and 

 grauwacke slate, or transition slate if you please, as the period is, in 

 point of fact, all we contend about, in your Number for July, I 

 perceive the Rev. Mr. Conybeare met with the same appearances at 

 Clovelly, on the north coast of Devon ; and if that be not suffi- 

 cient, i lieg leave to refer you to the magnificent specimen of slate, 

 from Tentagel, in Cornwall, presented to the Geological Society, 

 covered witli the impressions of shells — it speaks for itself. 



Article VI. 



Outlines of the Mmeralogy of the Ochil Hills. By Charles 

 Mackenzie, Esq." F.L.S. F.W.S. M.G.S.f 



(With a Map.) 



If the true ends of science be promoted rather by careful obser- 

 vation than by vague hypothesis, the geognosy of Werner has 

 peculiar claims to admiration. Without the lofty pretensions 

 which constitute the chief distinction of some speculations, it has 



• The distribution of petrifactions seems to follow a regular law, wliicli it 

 •hould' be our object to trace. Pe(rifactions occur in transition limestone, but 

 hilhertd!, as far as I know, no slielU have been found in that rock, nuv any thing 

 else except madrepores and orthoceratites. It is, therefore, an object of consi- 

 derable consequence to examine carefully the Plymouth limestone, because if Mr. 

 Playfair's obseryafiou be verified it will establish a new fact of considerable 

 importance. Shells have been found in tran-sition slate; for I saw a venus which 

 Dr. Leach look out of a rock of that kind at Plymouth. Tlie point in discussion 

 uould not alter our opinion respecting the rocks in question ; but it would add t* 

 •ur knowledge of the distribution of animal petrifactions. — T. 



+ Read before the Wernerian Society of Edinburgh Nov. 14, 1819, 



