34 



fuccefs in his profeflion) informs me that they commence near Murlogh, 

 where my tour on that fide ended; that they are very numerous about 

 Torr point, Garron point, and in general on all projecting points on 

 that coafl: ; and he conceives (I think judicioufly) that points being found 

 where the Dykes are moil numerous, arifes from the proteftion they 

 give the land in thofe places, preventing the fea from making the fame 

 inroads there it did on the adjacent parts. 



Doftor M'Donald and I examined together the Dykes at White-houfe 

 point four miles from Belfaft ; feveral of them are crowded together, 

 three or four run parallel in an E. S. E. direftion at about one hun- 

 dred and fifty yards from each other, and are in one place croffed by 

 another at acute angles ; feveral of thefe Dykes, (I am told) are traced 

 acrofs the county of Down on the oppofite fide of Belfaft lough. 



Though thefe Dykes were fo near, yet they differed materially from 

 each other; in many the middle part and the fides were not of the fame 

 grain, nor conftituted on the fame principle; in fome we found zeolite 

 in the centre, but not in the fides, in others the middle part was formed 

 by cutting it acrofs (no doubt into prilms), while the fides were a rude 

 mafs fludded with coarfe round flones, about the fize of an eighteen 

 pound ball ; thefe lafl: Doftor M'Donald affured me he had often broken, 

 and found them compofed of concentric fpheres, like the pellicles of an 

 onion ; fome of the Dykes were of folid maffive prifms laid quite acrofs, 

 while one or two had a longitudinal divifiou running through their middle, 

 as in the fecond Dyke at Fairhead, 



In all the lines mai-king the conftruftlon of the Dykes, whether ac- 

 curate or faint, were acrofs at right angles to their dhrections, but the per- 

 fection of the workmanfiiip was very different, and when we attacked them 

 with a light fledge, we found fome to crumble, being in a flate of decompo- 

 fition, others refilled our efforts, while fome broke into fmall quadrangular 

 prifms, like the Dykes at Port Spagna and the Giant's Caufeway. 



. Doflor IvI' Donald fhewed me in his cabinet prifms he had taken from 

 a. quarry (no doubt a Dyke) near Belfafi: ; they were nine or ten inches 

 lung, and entirely compofed of triangular pyramids of the fame length, 



put 



