86 Dr. Mac Culloch's Sketch of the 



In the same place I found nodules of great size, and of a variety 

 which is far from common, but which has I believe been found in 

 the Faroe islands. The nodules in question are either hollow or 

 solid, and sometimes reach the enormous dimension of four and 

 even five feet. The hollow ones are crystallized within in the fas- 

 ciculated forms already described. The peculiarity of this variety 

 consists in its extreme frangibility : the least effort is sufficient to 

 detach the plates of which its structure is formed, and it therefore 

 falls to pieces in the very act of procuring it, unless great care is 

 taken ; its fracture is fresh, and distinguished by an uncommon 

 degree of the pearly lustre which is so characteristic of this mineral. 

 So great is its frangibility, that the jarring of the hammer at one 

 end of a large nodule is often sufficient to destroy the whole ; and 

 it not unfrequently happens , that when a large piece is obtained 

 entire and has been laid down, although it appears uninjured and 

 resists a strong effort of the hands to break it, yet in a few rninutes 

 it falls to pieces with a sort of violence not unlike that which is 

 known to happen in unannealed glass that has received an injury. 

 This variety is sometimes white, and much resembling spermaceti 

 in its translucency, but in the greater number of cases it is of a 

 delicate flesh colour. 



The next of these minerals is mesotype, and it is found in three 

 states, a compact, a mealy, and a crystallized form. Of these the 

 compact varieties sometimes recede so far in character from the 

 mineral in its most acknowledged forms, that it is only by tracing 

 the gradation of the several varieties, that we are enabled to de- 

 termine the names of those which occupy the distant points of this 

 range. The opake whiteness, the toughness, and the radiated 

 disposition of those specimens which may be considered as forming 

 the first remove, serves to connect them with the best characterized 



