134 REV. J. C. ATKINSON ON THE MINERALS OF BERWICKSHIRE. 



imperfectly crystalline shape, and a dull green colour, with nearly 

 the texture of a very fine sandstone. This, also, is nearly pure 

 silica. 



But what is this which' looks not unlike petrified salmon ? It 

 yields readily to the nail, and is evidently gypsum. We shall find 

 it in situ close by ; for, unlike the other substances which have 

 come under our observation and hammers, it is a native of the 

 place. There, you see that white band at nearly the bottom of 

 the bank — cliff I might almost call it ; that is its native bed. On 

 examining it closely we find a vein of white fibrous gypsum, of which 

 the fibres run obliquely, and which, from the thickness of 1|^ inch, 

 thins out in many places to nothing. Above it is a quantity of 

 the same mineral in layers, and more crystalline ; selenite, in short, 

 of a greenish-brown hue when split. Above that again a stratum 

 of shale, and then we come to the petrified salmon, which occurs 

 in lumps rather than in continued strata. Break one of these 

 masses, and you find the structure is all crystalline, though, for 

 the most part, the crystals are so minute, that it almost passes 

 into granular gypsum ; and most irregular, as you see, is the di- 

 rection of the veins of more distinct crystals. On the outside the 

 crystalline structure is far more apparent ; and, with care, you may 

 procure a plate of 1|^ inch in diameter. Close by you see a seam 

 of compact rock, of a dull grey colour. Massive gypsum is that. 

 See how, in one point of view, it skimmers from the play of light 

 upon those numerous but very small included crystals ; see, too, 

 this fallen rock, with cavities divided into cells as it were, some 

 of them containing sand tinged with iron, and cemented by means of 

 some other substance. That substance, too, is gypsum ; and those 

 cells not unfrequently contain specimens of red gypsum, externally 

 set as full of sharp dog's-tooth crystals as a tipsy-cake with almonds; 

 and here and there, in a very friable part of the rock, you may 

 find large detached lumps of the same kind of gypsum. I have 

 every reason to believe, that wherever a fissure in the rock permits 

 it, the white fibrous gypsum is still in process of formation ; and 

 I cannot but think, that supposing terrestrial electricity or electro- 

 magnetism to be the active agent in causing minerals to assume 

 their crystalline forms, careful experiments, not too few in num- 

 ber, made in such fissures, and accompanied by equally careful ob- 

 servation of the singular irregularity of the more crystalline veins 



