S76 Account of the IVIiynn Dykes in the 



horizontal strala, and when t a posed to the air hardens al- 

 most to the consistence of stone. 



At the contact the basalt and freestone were stronglv 

 united together, and for two or three inches the basalt had 

 in some sort acquired the colour and grain of the sand- 

 stone : I was particularly attentive to this fact, as Mr. Wer- 

 ner alleges the transition of basalt into other stones, and 

 Mr. Jameson found in Arran (pages 131 and 135) basalt 

 sometimes mixed with, and at others penetrated by, sand- 

 stone; but on this occasion Dr. M'Donald, by some ex- 

 periments, found that notwithstanding the freestone ap- 

 pearance the stone remained pure basalt. 



The basaltic area, from the north and east sides of which 

 these singular walls diverge in such abundance, compre- 

 hends a considerable part of the country of Derry, and 

 a much greater of the county of Antrim ; its breadth varies 

 from 20 to near 30 miles, and its length exceeds 35 ; it 

 seems composed almost exclusively of vast and steady ba- 

 salt strata accumulated upon each other; in one' place wc 

 count 16, in others we conjecture more, especially at Ma- 

 gilligan rock, as wc know the basalt to be 1200 feet deep 

 there. This whole mass rests upon a vast stratum of while 

 limestone about 200 feet thick, of the same extent with the 

 basaltic area, but discoverable only at its periphery, which 

 extends above 80 miles. 



This mighty stratum ascends to the southwad, until its 

 lower edge acquires on the east side a height of 800 feet, 

 and on the west at least 1700; the country below the 

 limestone stratum, and without it, is on the west sitle 

 mostly schistus, on the east sandstone and clay peneti^aled 

 by basalt dykes, which furnish stones in abundance for all 

 purposes. 



The Scotch whvnn dykes have been generally supposed 

 to originate m Ireland. If this f;ict be admitted, we can 

 easily trace them by attending to the directions of our own; 

 thus those that issue from the coast west of Ballycastle, 

 proceeding north with a slight inclination to the east, are 

 to be sought for in Islay, Jura, Mull, 8cc., where Mr. Mills 

 actually found them in great numbers. 



Our dykes which are seen at.Murlog, Torr, and Cushen- 

 dun, are obviously those which, having crossed rhe Mull 

 of Cjutyre, were observed by Mr. ^ajiieson in such abun- 

 dance in the Isle of Arran. 



Dr. Hutton also mention* 20 or 30 whynn dykes he 

 found '* in the shifc of Ayr to the north of Irvine on the 

 coast," These correspond with the numerous dykes about 



Gar roil 



