432 ON THE GEOLOGY OF THE 



sometimes, though very rarely, a marly ferruginous matter in- 

 terposed between them, but I have not observed it of more 

 than two or three inches in thickness ; it is very much given 

 to decompose. 



Of this limestone there is another variety, of a dark-brown 

 colour, extremely compact, with the vitreous texture of our in- 

 durated sandstone, or the Felspath cero'ide of the French : it is 

 less common than the others. 



In the first limestone, I have found flint, not generally, but 

 very frequently ; and where the rocks were well exposed, I 

 have seen the nodules tracing their line along the centre of 

 the beds, exactly in the same manner as in the white limestone 

 of Antrim, or among the chalk cliffs of the Isle of Wight. 

 Organic remains do not frequently occur in it: they are found, 

 however, and in one spot in remarkable abundance. The dif- 

 ferent organised bodies I noticed, are a cornu ammonis, an echi- 

 nus, a pecten, and coralloids ; all but the last in single detach- 

 ed specimens ; but the coralloids abound at a spot about 150 

 yards east of the Lighthouse on St Hospice. It is curious to 

 observe the effects of the weather on the surfaces of some of 

 the blocks of this limestone. The substance of the petrified 

 organized bodies being harder, they have resisted the action, 

 while the matter in which they were included has been washed 

 away ; so that in some places the corals may be detached, quite 

 relieved from the paste which once enveloped them, and form- 

 ing a net-work on the surface, not unlike what we often see in 

 the branches of ivy on the surface of a wall. 



Near this, there are two or three other strata which are 

 crowded with the remains of corals, fragments of the shell of 

 the echinus, and various other debris. These particular beds 

 resemble some of the limestones of England, having the or- 

 ganised bodies crystallised, and inclosed in a paste of compact 

 limestone. 



This 



