21 



TAB. CCCXV. 



J he present curious production is one of those things 

 that few can expect to possess ; therefore it is, like many 

 others in this work, a pleasant proof of the utility of figures, 

 which is certainly next to the possession of the object, as to 

 the instructive information it gives, and the making public 

 those beauties of Nature that must otherwise be ever lost 

 to the scientific world. 



I do not know that this formed Crystal has yet been 

 spoken of: Rome De Lisle and Haiiy do not mention it. 

 It is in the shelly Limestone which forms one of the upper 

 strata of Derbyshire that this has been formed, hid from 

 mortal ken, within one of the most remarkable species 

 of shells I ever knew, Conchy Holy thus productus of Mr. 

 Martyn's most ingenious work, plate 22. f. 1,2, 3. 



The reason why the primitive molecules should so form, 

 remains a desideratum. We have but just got a notion of 

 the subject, but diligence in this discovering age may yet 

 learn more of Nature's ways, and even this may be the 

 leading cause : the equally contrariwise attraction of the 

 particles may be governed by the equal evaporation of the 

 fluid in contrary directions, and the gravitation of the sol- 

 vent medium may poise them to that angle which so nicely 

 replaces them. 



One great curiosity of this Mackle is, that the lateral notch 



