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XL — On certain Vegetable and Mineral Formations in Calcareous Spar. 

 By Sir David Brewster, K.H., D.C.L., F.R.S. (Plate VII.) 



(Read 28th April 1862.) 



When occupied several years ago in studying the fluid and gaseous cavities 

 in minerals, my attention was drawn to certain remarkable formations in per- 

 fectly transparent specimens of calcareous spar. These formations were of two 

 kinds — the one apparently of vegetable origin, and the other obviously mineral. 



1. The formations that appeared to be of a vegetable nature occur in speci- 

 mens of calcareous spar from King's County, Ireland, and had been deposited on 

 the faces of the primitive rhombohedron during its formation. The general aspect 

 of the substance is that of a plant. Its colour is a dark green, which becomes 

 lighter, and very brilliant, when the specimen is viewed by reflected light. These 

 different effects, and the general structure of the substance, are finely shown in 

 the accompanying drawings, executed for me by the Hon. Mrs Ward. In the 

 figures magnified 60 diameters, a great number of minute spheres are seen scat- 

 tered up and down among the stems and branches of what has every appearance 

 of being a plant. They are more distinctly seen with a magnifying power of 100, 

 and in the drawing, made with a power of 420, one of them has apparently burst 

 and discharged its contents, as if it had been a seed-vessel, as shown in Plate VL, 

 fig. 6. With the same high power the stems are distinctly tubular. 



As the microscope could give me no further information respecting this in- 

 teresting substance, I submitted specimens of the spar to my distinguished friend, 

 Mr Andrews, Professor of Chemistry, and Vice-Principal, in Queen's College, 

 Belfast, who favoured me with the following analysis of the extraneous sub- 

 stances : — 



" The extraneous matter in the specimens is entirely destroyed by heating in a 

 glass tube to incipient redness— a small quantity of water, having a strong empy- 

 reumatic odour, being at the same time given off. It dissolves in strong hydro- 

 chloric acid, without leaving any residue, but colours strongly the acid. Hence 

 the extraneous substance appears to be of organic origin." 



2. In another specimen of calcareous spar from India, the extraneous mat- 

 ter is arranged in fine parallel lines, which are generally, though not always, 

 parallel to the faces of the rhombohedron. In order to determine its nature, I 

 submitted the specimen to Professor Andrews, who obtained the following 

 results : — 



" I selected," he says. " two clear specimens, and placed them in hydrochloric 



