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The ISTatukalist. 



and origin of this remarkable outburst of igneous rock, which extends 

 in nearly a straight line from the neighbourhood of Middleton, in 

 Teesdale, to a short distance south-west of Whitby. It is assumed by 

 some eminent geologists that the Dyke is associated with what is known 

 as the Whin Sill, and which has its maximum development in the vicinity 

 of High Force and Cauldron Snout, as an interbedded igneous rock, 

 agreeing in general lithological characteristics with the stone of the Dyke, 

 but differing from it essentially in its relation to the stratified deposits. 

 In the case of the Whin Sill, the igneous rock occurs as a layer obtruded 

 between the members of the upper carboniferous series (the Yoredale 

 rocks of Phillips). The Dyke, however, cuts through the superincumbent 

 strata vertically, and, during its course, penetrates stratified deposits 

 from the carboniferous to the oolitic age. I am disposed to agree with 

 those geologists who regard the Whin Dyke as quite distinct in its origin 

 froin the Whin Sill. It has now been conclusively demonstrated that 

 even so late as the miocene period, which represents a comparatively 

 recent geological epoch, the north-western portion of Great Britain was 

 the theatre of most active volcanic phenomena, when in the Island of 

 Mull, and in other j)arts of the Hebrides, all classes of igneous rocks, 

 from granite to the representatives of the most modern volcanic minerals, 

 were poured out in vast abundance. It would seem, then, more rational 

 to connect the Whin Dyke with this latter period of local volcanic activity 

 than with the infinitely older carboniferous era. Geologists now know 

 that the age of any particular igneous rock is not to be deduced from its 

 mineralogical or lithological composition, as the various forms of highly 

 crystalline to compact varieties are merely due to the conditions under 

 which the cooling process has taken place — the granites and basalts of the 

 tertiary period being lithologically undistinguishable from those associated 

 with the oldest sedimentary deposits. The Whin Dyke ai^pears to have 

 altered the rocks through which it penetrated, only a short distance on 

 each side. But after all is said, the remarkable fact remains that we 

 have here the occurrence of a mass of igneous rock that strikes across 

 half-a-dozen formations in what is virtually a straight line, and which 

 varies only to a slight extent throughout its whole course, either in 

 dimensions or in mineralogical composition. The amount of disturbance 

 that this outburst has exercised on the strata penetrated is remarkably 

 slight. — At the meeting at Forcett. the members had an opportunity of 

 inspecting a surface of mountain limestone, shewing, in a most unmistake- 

 able manner, strige and markings due to the movement of ice during the 

 glacial period. Specimens of Shap Fell granite were also found in situ. 

 There is no doubt that during the glacial epoch there was an ice flow over 

 Stainmoor, which branched off in various directions. The ice that has 

 marked the Forcett limestone appears to have been moving in a south- 

 easterly direction, as all the strise tend that way. The limestone workings 

 at Merrybent were also visited, but considerable doubts were expressed 



