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AN OUTLINE OF THE GEOLOGICAL HISTORY 

 OF UPPER SWALEDALE. 



J. G. GOODCHILD, H.M. Geol. Survey, F.G.S., F.Z.S., M.B.O.U. 



The rocks of Swaledale consist chiefly of the Lower Carboniferous 

 Series, i.e., the Yoredale Rocks and the Mountain Limestone. 

 Detached remnants of the basal members of the Millstone Grit, now 

 represented only by outliers of the Kinder Scout Grit Series, and the 

 beds above this up to the base of the Third Grit, also occur on the 

 hill tops in places. The whole of the Carboniferous rocks of this 

 area are of marine origin, and represent thalassic deposits laid down 

 in connection with the delta of a large river, which drained part of a 

 continent lying far away to the north-west. During a prolonged, 

 but slow, subsidence, occasionally varied by slight movements of 

 upheaval, or by pauses when no movement took place, the delta 

 referred to gradually advanced its seaward margin in a south-easterly 

 direction ; but the rate of advance was so slow that it was not until 

 near the close of the Yoredale period that the delta itself actually 

 reached this point. Prior to that event the strata deposited here were, 

 at first, mainly organico-chemical (limestones). Then, as the delta 

 approached somewhat nearer, alternations of limestones, sandstones, 

 shales, coals, and cherts were left, piled one above another in regular 

 layers to a considerable thickness. Finally, when the old delta had 

 pushed its way seaward so far as to actually reach this part, little 

 else than grits, shales, and coals were laid down, the deeper-sea 

 deposits and those proper to clear water being, of course, wanting. 

 But while these conditions obtained in what is now Swaledale, 

 deeper water and clearer water conditions still prevailed miles away 

 towards the south-east, and were, in their turn, pushed still farther 

 out to sea as the delta grew towards them. 



This preliminary explanation will enable us to understand how it 

 came about that the lowest marine beds of the Carboniferous period 

 consisted almost exclusively of limestone here ; and how it happened 

 that, as we trace the succession of the rocks upward, we find, on the 

 whole, the relative thickness of the clear-water deposits to those of 

 detrital origin becoming less and less, until, when we reach the 

 Millstone Grit, true limestones are hardly to be found at all. 



The rocks of the upper parts of the dale consist chiefly of the 

 Yoredale rocks, so named by Prof. Phillips from Yoredale or the 

 dale of the Yore (VVensleydale), where strata of this age are well 

 exhibited. The Yoredale Rocks may be described as consisting of 



August iSgo. 



