Dr. Berger on the Isle of Man. 43 



with crystallized calc spar. As the texture becomes more compact 

 it gets harder and of a more intense colour, approaching to black ; 

 the fracture at the same time approaching to conchoidal. Iron 

 pyrites dispersed through the mass is not uncommon, and when 

 scratched the smell of sulphuretted hydrogen is rendered sensible : 

 it burns very white, a circumstance which shows that the colouring 

 matter, being volatile, is of an animal or vegetable origin. In diluted 

 muriatic acid it makes a rapid and brisk effervescence, leaving 

 rather a considerable residuum. The mean specific gravity^, as 

 resulting from eight specimens, I found 2,704. 



I am not aware that the dark marble-limestone of Pool-vash 

 contains organic remains ; I have seen stripes or veins of lamellar 

 and greyish limestone full of petrifactions alternating with the 

 darker variety that remained quite freed from those exuvise. 



Thin and crumbling strata intervene between the solid strata of 

 limestone. They are called Soles in the Isle of Man, but generally 

 Partings among the miners. 



The magnesian limestone in the places where it occurs, differs 

 enough in ieself to induce me to give a particular description of it. 

 At Cass-ny-HaWin it is either finely granular or in lamellar and well 

 determined crystals. In the latter case it abounds with small ca- 

 vities filled with crystallized rhomb spar, the crystals of which 



the tliickncss of the strata bf\Ti's a more equal proportion to the length or respective 

 distance of the dip-joints, (he natural divisions will come to a cubical form. If on the 

 contrary, the structure be thin-slaty, the rocks will rise spontaneously under the form 

 cither of ^rt^y or slates. Whatever may be the shape of these natural blocks, their tAvo 

 contiguous sides are constantly coated with the predominating ingredient of the rock 

 itself in its present state. Thus if the rock be quartzose, the coatings of the dip-joiut>; 

 will be veins of pure white quariz; if it be calcareous, the coatings will be crystallized 

 calcareous spar, but unless we cause artificially tiie splitting of the rocks to fake place, 

 seeing but a vertical or a horizontal section of the coatings, we arc apt to adopt the 

 wrong opinion they arc veins instead ol laj/crs. 



F 2 



