.[ 364 ] 



LVII. Account of the IVhynn Dykes hi the Kt'ighhourhood 

 of the Giant's Causeway, Batly castle, and Belfast : in a 

 letter to the Lord Bhihup of Droniorc, fro7n William 

 Richardson, D.D» late Fellow of Trinity College, 

 Duhlin^, 



^1t Lord, W hen I last had the honour of conversing 

 with you on basalt subjects, you were surprised when I 

 told you that the whynn dyhcs^ whieli of late have so much 

 occupied the attention of naturalists in the western isles of 

 Scotland, originated on our Irish coast, and t'Bpecially 

 about the Giant's Causeway. 



As your lordship expressed a wish for furtlier informa- 

 tion of the subject, I promised to communicate to you 

 •such observations as J should make when I had examined 

 the coast a second time, in order to ascertain i\\Q facts with 

 the utmost precision. 



Previous to my entering into a particular account of our 

 dykes, I will take/ the libcrtv of making a few general ob- 

 servations on those in both countries. 



The whynn dykes in the Hebrides are seen under very 

 iliflferent circumstances fron> those on the northern coast of 

 Ireland, There they are found on, and above, the surface, 

 generally a few feet; and often serve as fences, whence 

 they obtain their najue. In this form they run northwards 

 quite to the extremity of these islands, ascending and de- 

 scending mountains, crossing seas ; and where these are 

 narrow, the dykes that run into the water at one side of a 

 channel, are seen rising out of ii at the other side, steadily 

 pursuing their formed rectilineal course. 



With us they are sometimes exhibited in a very different 

 manner. Their first appearance is in the faces of our vast 

 perpendicular precipices, where they are seen cutting ver- 

 tically the several strata of which these are composed, and 

 then burying themselves in the northern ocean. 



The observations made on these whynn dykes in the two 

 countries, taken together, make our information on the 

 subject complete. In the Hebrides we are surprised at 

 the incredible length to which these mighty walls proceed, 



* Dr. Richardson's paper on the Basaltic Country in the Counties of 

 Derry an<l An'irim, published in owr 3;3d vol. has excited so much attention^ 

 that I am persuaded I shall render an acceptable service to geologists hy 

 giving: in the Piiil. Map. some previous papers by tiie same o^entlcman, pub- 

 lished iu the Transactions of ihe Roynl Irish Academy, 'ilie present paper 

 ii from their 9th volume. — Ecir. 



and 



