Ohfirvaivns on iht Bafaltk Coaji of If eland. 315 



fubordinate internal principle of conftruQion, the great prifms breaking into fmaller } co- 

 lumnar bafalt has rarely this property, I have- found it only in the pillars I (hewed you at 

 Ballylagan) and at the eaft fide of Fairhead, but all the gaws or dykes feem to be con- 

 ftru£led upon this principle, and the two ftrata which alternate fo frequently at Portrufh 

 poflefs the fame property in an high degree, and one of thefe you and your friend Mr. 

 Chenevix have proved by analyfing it, that it is pure bafalt. 



To return to Fairhead, immediately below the Grey Man's Bath, a new ftratum of co- 

 lumnar bafalt begins to appear, and contrary ^o what I have obferved every where elfe, not 

 parallel to the one above it (which feems nearly horizontal) but dipping to the fomh-eafl?, 

 of courfe as we advance in this direction thefe ftrata diverge from each other, and the in- 

 creafing fpace between them is fitted up with new mateiials, to wit, alternate ftrata of 

 free ftone and coal. 



Thefe ftrata are all parallel to the lower columnar ftratum ; the one immediately refting 

 upon it is coa!» this is the vein that was laft wrought at Murtogh, and the adit to the 

 mine runs in along the heads of the bafalt pillars. 



On tracing thefe alternate ftrata in a weftern dire£tion, they are found to terminate fuc- 

 ceflively againft the bales of the upper columnar ftratum, always making with it an angle 

 equal to that of the inclination of the two great ftrata. 



Here we have probably the ftrongeft inftances that have yet occurred any where of the 

 contads of coal with columnar bafalt, for while the loweft ftratum of coal refts with its 

 whole furface on the heads of bafalt pillars, every ftratum of coal above it comes by regu- 

 lar fucceffion into contaft with the bafes of the pillars of the upper columnar ftratum. I 

 ihuft confefs I did not examine thefe contafbs, the acclivity was fo fteep, and fo ftrewed 

 with enormous mafles of rock as to be inacceflible at leaft to me. 



You muft obfervc that the ftrata at Fairhead totally differ both in materials and ar- 

 rangement, from the ftrata compofing Bengore Head, which we counted together, and 

 found to be 16 in number; in truth no two of our vaft precipices, whether hanging over 

 the fea, or in the interior of the country, perfedly (or I may fay nearly) rcfemble each 

 other in thefe circumftances. 



, This variety in the ftratification of our bafalt country, muft be a fubje£l of much curio- 

 fity, particularly togeologifts, and was no doubt confidered as fuch by Mr. Whitehurst 

 and MiLLs» when they promifed in their title pages an account of our ftrata, yet in the 

 body of their worksforgot the topic. 



If you can find leifure for another excurfion fo far north next fummer, our ftrata will 

 aftbrd us an ample fund of entertainment, both in trying the theories of cofmogonifts by 

 the left of thefe ftrata, and in conjefturing from their interruptions and other circum- 

 ftances^ what changes our globe has undergone (ince its creation. 



I am, SIR, I 



Your very humble Servant, 



WILLIAM RICHARDSON, D. D;. 

 ClonfeeleHoufe^yios, 03^22, 1801. Late Fellow of TrinityCo/lege, Dublim 



Obfervationp 



