4 ACCOUNT of a MINERAL 



1 791, I commenced and executed a feries of experiments, the 

 detail of which I laid before the Collej2;e Literary Society of this 

 place in March 1792. '1 hefe not only fatisfied me that I had 

 been right in my conjedure, which was, that this mineral dif- 

 fers from ai-rated barytes but alfo gave reafon to imagine, that 

 it contains a peculiar and hitherto unknown kind of earth. 

 Other experiments, more lately performed, ftrongly confirm, 

 and perhaps 1 may add, eftablilh this notion. 



Dr Crawford, having remarked the confpicuous difference 

 in the form of the cryftals of the muriate of this foflil and of 

 the muriate of barytes, and in their folubilities in water, has 

 thrown out a conje(5lure to the fame purpofe. at the end of his 

 paper on the Muriated Barytes, in the fecond volume of the 

 London Medical Communications. 



2. The mineral of which 1 have been fpeaking, I am in- 

 formed, is found in the lead- mine of Strontian in Argyleihire. 

 It lies imbedded in the metalliferous vein, fcattered among the 

 ore and the different fpecies of fpar that are moft commonly 

 met with in fuch fituations. I have fpecimens in which por- 

 tions of lead-ore are attached to this mineral, and others in 

 which it, calcareous and ponderous fpars, are intermingled in 

 large and confiderable maffes. 



More obvious ^alities. 



3, The appearance of this foffil varies in different famples. 

 It univerfally poffeffes the fparry ftrucflure, and fometimes 

 bears a flrong refemblance to fome forts of calcareous or fluor. 

 fpars. Its texture is commonly fibrous. The fibres fometimes 

 are flender, and in ciofe contadt with each other, fo as to give 

 the mafs a confiderable degree of compadnefs. At other times 

 the fibres are much more grofs, and affume a kind of columnar 

 appearance. The fibres or columns have, in the greater num- 

 ber of fpecimens, a degree of divergency, ilTuing as radii from 



