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Notes on some rare Scottish Minerals, By Professor L. A. 

 Necker of Geneva. Communicated by the Author. 



1. Crystallized hydrate of magnesia occurs at Swinaness, in 

 the island of Unst. The crystals are small hexagonal tables, 

 which are parallel to the lamellae of the lamellar specimen of 

 hydrate of magnesia, of which they form part. These are 

 very short six-sided prisms, having their three alternate termi- 

 nal edges truncated by planes which are oblique to the axes, 

 thus seeming to indicate a rhomboid as the primitive form of 

 this mineral. I did not find the specimen myself, as the vein 

 is now exhausted from which this substance was formerly ob- 

 tained for collections, but I procured it from a native of the 

 neighbourhood of Swinaness, who had collected it. On one of 

 the small crystals, there are feeble traces of an oblique face on 

 the terminal edges, which are not modified in the others. 



2. Arragonite crystallized in simple forms occurs, lining the 

 walls of a small fissure, in the serpentine of Swinaness. The 

 crystals are rhomboido-prismatic, are terminated by diedral 

 summits (sometimes by four-sided pyramids ?), and are placed 

 on their matrix parallel to one of their lateral edges, or to one 

 of the sides of the prism. They are accompanied and covered 

 by a yellow translucent matter, which seems to me to present 

 passages to the white aragonite, and which effervesces with 

 acids. Is it not a ferruginous aragonite, or the jimokerite of 

 Dufrenoy ? The prisms of aragonite of Swinaness have six or 

 eight sides. 



3. Gallinace of Beal in Skye. — This massive mineral, or ra- 

 ther this apparently homogeneous rock, has been taken for a 

 retinite or pitchstone by Messrs Murchison and Sedgwick, in 

 their excellent description of this part of Skyo ; and nothing, 

 indeed, can bear a greater resemblance to pitchstone than this 

 substance, but it differs essentially from it in its specific gra- 

 vity, and by its fusion before the blowpipe into a black sco- 

 riaoeous enamel. It forms a crust or rind of two or three 

 inches in thickness, on a basaltic dyke, which traverses the 

 whole valley of Beal, like a prominent wall composed of hori- 

 zontal prisms. Probably the vitreous crusts of the dykes of 



