﻿458 Henry E. Hoicorth — Geology of the Isle of Man. 



town Bay is occupied by a famous basaltic boss, known as the Stack 

 of Scarlet. From this boss lines of trap emerge in sporadic fashion 

 and may be traced in various directions, especially about the pro- 

 montory of Langness, in Derbyhaven Bay, and. at Cushnahavin. 

 Where they have burst through, they have naturally altered the rock 

 very considerably. It has in some places so altered the limestone 

 that it is impossible to see any limit where trap ends and limestone 

 begins. In another place, namely, close to Konaldsway, between 

 high- and low-water mark, it has broken it up into rhomboidal 

 blocks by cracks running S. 40° W, and S. 30° E. But the meta- 

 morphism is more important elsewhere. Let me quote the graphic 

 words of Mr. Gumming himself : 



" There is one remarkable fact which should not be overlooked, 

 which is, that the Boulder-clay itself seems in some measure to have 

 partaken of the metamorphosed character of the limestone. Patches 

 of it here and there are hardened and cemented, and. present a 

 baked appearance, and have resisted the action of the sea. It is 

 difficult to determine whether this has resulted from long contact 

 with the ochreous mass of altered limestone, or from the escape of 

 heated gases at some period of the Boulder-clay through cracks 

 formed by the previous disturbances which we must thence class as 

 belonging to the Boulder period." (op. cit. p. 100.) The difficulty 

 suggested by Mr. Gumming exists only so far as I can see because 

 of his classing the red conglomerate as Devonian. If he had seen 

 that it was in fact but an altered glacial deposit, but one conclusion 

 would, it seems to me, have been possible. Let me, to illustrate my 

 position, quote one more passage, and although a long one, it shall 

 be the last. Speaking of the great trap dyke at Langness, Mr. 

 Gumming says : — " The ground jolan of it is well worthy of a 

 minute study, and the contrast of colour of the two rocks (the 

 green or olive-coloured trap and the red conglomerate) renders the 

 phenomena distinctly visible to even an ungeological eye. The trap 

 seems to shoot out in one strong body from the schist to the east- 

 ward, and may be seen as a dyke of the breadth of forty-five feet, 

 where it runs out to sea, on the eastern side of the peninsula ; but 

 as soon as it enters upon the old red conglomerate {sic) which over- 

 lies the schist, we find it separating into branches and twisting about 

 amongst the pebbles and boulders of that formation in a most 

 singular manner. Some of these branches taper oif to an extreme 

 thinness. We can trace them by the colour till they are scarcely 

 the thickness of a wafer. Now on the opposite side of the bay, at 

 Knockrushen, we see this dyke where it cuts through the limestone 

 in the same solid and compact form which it has where it cuts 

 through the schist. There are there to be sure two or three straight 

 cracks in the limestone, which have been filled up by the fluid trap 

 injected from this dyke ; but the general fact which we must observe 

 is this, that in the schist and tough limestone the trap dyke is com- 

 j)act ; in the old red conglomerate it is spread out and branching. 

 And thus we come to the conclusion that the fluid trap was forced 

 upwards with enormous force through the schist ; that when on its 



