1852.] NICOL ON THE GEOLOGY OF CANTYRE. 417 



from half an inch to 3 or 4 inches, which is far more than mere eon- 

 traction could produce. It seems, therefore, necessary to suppose, 

 either that the veins of haematite were segregated from the rock 

 contemporaneously with the formation of the columnar structure, or 

 that after their formation the prisms were somehow forced asunder, 

 and the vein-matters introduced between them. The latter appears 

 to me the more probable hypothesis of this very curious formation. 



The facts just mentioned relative to these igneous rocks show that 

 they not only differ much in mineral character, but also have been 

 formed at very different periods. Some are probably more ancient 

 than the red conglomerate or coal-formation ; others are contempo- 

 raneous with these beds ; others again were produced after their de- 

 position, whilst a fourth group even intersect the latter as veins. 

 Their mode of occurrence also differs very much ; some appearing as 

 huge domes or prisms pushed up through the strata ; others as over- 

 flowing or intercalated beds ; and others as veins or dykes filling 

 cracks or fissures in the older formations both stratified and ig- 

 neous. 



In Dr. MaccuUoch's map of Scotland, part of the valley west of 

 Campbeltown is coloured as Lias, and the same formation is marked 

 as occurring in this locality in most of the recent geological maps of 

 the British Islands. After a careful examination of the district, I 

 have not been able to find any indications of the Lias formation. 

 The plants in the coal-beds now wrought are, as formerly noticed, 

 only those of the true Coal- formation, and no trace of lias fossils was 

 observed either in the rocks themselves or in the detritus of the 

 country. In the sandstones and limestones connected with the trap- 

 rocks organic remains appear to be wanting, but the general charac- 

 ter of the beds and their relation to the undoubted carboniferous 

 strata, left no doubt in my mind that they were portions of this 

 rather than of any more recent group of rocks. It thus appears, that 

 the Lias must be obliterated from this portion of the geological map 

 of Scotland. How it ever came to be introduced is not readily ex- 

 plained. In his * Mineralogical Travels,' Professor Jameson describes 

 the beds as belonging to the Coal-formation. In his work on the 

 Western Isles*, Dr. Macculloch says that the coal wrought near 

 Campbeltown is a portion of that of xlyrshire. In the same place, 

 however, he identifies it also with the coal underlying the trap in 

 Mull and Morven, and when the latter was proved to belong to 

 the Lias, he probably assumed, without renewed investigation, that 

 this was true in like manner of the coal at Campbeltown. 



The tract coloured in MaccuUoch's map as Lias, together with a 

 part of the red sandstone on the north, is, however, covered to a 

 great depth with recent deposits, partly at least of tertiary age. The 

 country between the Loch of Campbeltown and Machrihanish Bay on 

 the Atlantic is a low broad valley, known as the Laggan of Cantyre, 

 and so little elevated above the sea that a depression of 40 feet or 

 less would convert the whole southern part of the peninsula into an 

 island. This valley is filled by various unconsolidated deposits. The 

 * Vol, ii. ]). 71. 



