434 ON THE GEOLOGY OF THE 



fragments, and in caverns, in massive columns, we find a 

 great deal of that stalactitic limestone known by the name of 

 Antique alabaster, which is likewise found filling the rents, and 

 forming the cement of the Br6sche en place. The mode in 

 which this substance has been infiltrated, is finely exemplified in 

 the sections laid open in forming the new road above alluded to, 

 where cavities occur, in some respects very much resembling 

 those of calcedony, as seen in the trap rocks of Feroe, though on 

 a very different scale. The calcareous matter has been deposited 

 gently and slowly on the sides of the hollow, here and there 

 has fallen in stalactites from the summit, either disengaged in 

 columns, or along the sides, and then forming horizontal plat- 

 forms at the bottom, like the onyx in thousands of the pebbles 

 which occur in the amygdaloid of Scotland. Connected with 

 all these, however, is the vein by which the infiltration was in- 

 troduced ; and in this lies the distinction between those calca- 

 reous and the calcedonic geodes. 



Besides this species of cement, there are others, one of which 

 forms a very compact limestone, and often presents an even con- 

 choidal fracture, of a pale reddish-brown colour, and frequent- 

 ly dendritic ; this passes into a coarser variety, with somewhat 

 of a splintery fracture, and of a dark-red colour. There 

 are some very remarkable examples of the infiltration of this 

 material, where the great beds of limestone are not only as it 

 were soldered together, but where, having been broken down 

 into the smallest fragments, they are again consolidated, and 

 form the most compact masses. . Another cement is of a pale 

 brick-red colour, more earthy in its texture ; and when it forms 

 the base of the white variety of limestone, it has a very beau- 

 tiful and singular effect. The fragments are sometimes in very- 

 large masses, and sometimes in very minute particles. Where 

 exposed to the action of the weather, the cement is frequently 



washed 



