394 ON TKE FORMATION OF THE CHALK STRATA, 



This rock, while compared with others, is of rare occurrence ; 

 for although it be found in various parts of Europe, it does not, 

 so far as we know, exist in any of the other quarters of the 

 Globe. In the south-east of England it may be said to abound ; 

 and in the north-east angle of Ireland, the white limestone pre- 

 vails to a great extent. Its connection with other rocks has of 

 late years occupied the attention of Geologists, and it has been 

 found to be a member of a considerable series, as uniform in 

 position with respect to its members, as any of those which 

 compose the great system of Werner; and although* it be 

 among the earliest of this series, yet in England it very ge- 

 nerally occurs uncovered, while in Ireland it is almost always 

 overlaid by the trap rocks. In both, it uniformly rests on the 

 Green Sand or Mulatto-stone. 



The extent and position of the white limestone in Ireland 

 is somewhat remarkable. From Belfast it reaches all round the 

 coast, extending to Rathlin, and, with some trivial intermissions, 

 to Colerain ; and in a line to the westward of this, it runs south 

 through the middle of the county of Londonderry, to its verge in 

 the low lands which border Lough Neagh. On the west and south 

 of that lake it disappears ; but it occurs again to the south-east, 

 at Moira, in the county of Down, which connects itself with the 

 range in the neighbourhood of Belfast. In all this extent, the 

 limestone generally appears to dip inwards, so that within the 

 area of the space I have described, I understand it is nowhere 

 to be seen, although, from the position all round, there can be 

 little doubt that it exists. 



In England, it has also been observed, that there are two 

 distinct varieties of chalk, one of which is much harder than 

 the other ', occurs in a lower position, and contains no flints, or 

 at least very rarely. The stratification of this variety is marked 

 by seams of a greyish-coloured chalk, containing probably an 



admixture 



