300 



small, unless the contraction be very great in proportion, to the dia- 

 meter of the pipe. 



A Letter on the Alterations that have taken place in the Structure of 

 Rocks, on the Surface of the basaltic Country in the Counties of 

 Derry and Antrim. Addressed to Humphry Davy, Esq. Sec. R.S. 

 % William Richardson, D.D. Read March 17, 1808. [Phil. 

 Trans. 1808, p. 187.] 



The general design of this paper is to show the great distance to 

 which the same strata may be found to extend, or to have extended, 

 over the surface of a country, and thereby to explain the existence of 

 small detached portions of the same species of matter at considerable 

 distances from each other, as having been originally connected by 

 continuity of the same material over the whole surface of the coun- 

 try, whatever be the present interval, and whatever be the quan- 

 tity of matter which such an hypothesis supposes to have been re- 

 moved. 



The basaltic area which comprehends most part of the county of 

 Antrim and a portion of Derry, appears to Dr. Richardson peculiarly 

 favourable to such speculations, uncommonly regular in its stratifi- 

 cation, and highly favoured by nature in the frequent exposure of 

 the strata in their abrupt and precipitous terminations. 



In the island of Rathlin, more especially, the original features are 

 most happily displayed, and are still in good preservation. 



It is in the periphery at the northern side that the sections arc 

 seen to the greatest advantage, as the perpendicular fa9ades are often 

 continued for miles together. 



Of these facades, four are more distinguished for their grandeur 

 and beauty than the rest, Magilligan, Cave Hill, Fairhead, and Ben- 

 gore. The two former are the extreme points of the N.W. and S.E. 

 diagonal, and are forty miles asunder ; at the summits of mountains, 

 accessible by land. The two latter are visible only from the sea, but 

 are more diversified and more curious in their structure. 



The promontory of Bengore, which is nearest to the place of Dr. 

 Richardson's residence, has principally engaged his attention ; and the 

 minute description of its strata forms a considerable portion of his 

 memoir, for the purpose of showing the station which the Giant's 

 Causeway occupies in the arrangement of the promontory, and also 

 for the purpose of noticing several facts, which he thinks likely to 

 throw light upon the operations performed on our globe since the 

 period of its consolidation. 



In the order of the description, Dr. Richardson first gives a gene- 

 ral sketch of the promontory when approached from the west, with 

 an account of the inclination, ascent, culmination, and dip of its 

 strata. Of these he enumerates as many as sixteen, and observes 

 that these are all cut perpendicularly in eleven different places by 

 those mighty walls called in Scotland whyn dykes. 



These all reach from the top of the precipice to the water, out of 



