70 Marr : The Rigidity of North-west Yorkshire. 



headwaters of the Ure. The fault scarp of the Craven system 

 has caused the development of rivers flowing southward from 

 the highlands north of the fault. So far as I know, the some- 

 what complicated drainage of this tract has not been worked 

 out in detail. 



The simplicity of arrangement of the Carboniferous Lime- 

 stone has caused an underground drainage system of exceptional 

 interest to be developed. Much literature has been devoted 

 to this. So far back as 1871, Sir WilUam Boyd Dawkins gave 

 a detailed account of it in his book ' Cave Hunting,' and 

 now, thanks largely to the members of the Yorkshire Geological 

 Society, we have a mine of informa.tion available to the 

 students of Spelaeology. 



One of the most striking effects of the tract of high ground, 

 with its steep scarp to the west, is its operation as a barrier, 

 affecting both inorganic and organic nature. We may illus- 

 trate this by commenting upon its effects upon ice, plants and 

 mankind. We may regard the modern study of its glaciation 

 as dating from the publication of the well-known papers of 

 Tiddeman and Goodchild. They clearly established the 

 importance of the block as presenting a barrier to the 

 easterly movement of the ice coming from the west and 

 north-west. Since then, an important advance in our study 

 of glaciation is due to Kendall's classic paper on glacial overflows 

 in Cleveland. Dwerryhouse has applied the principles to a 

 study of part of the district under consideration, and Kendall 

 himself has recently outlined the events which happened on 

 the western borders overlooking Edenside, where the phenomena 

 are of very great interest. All geologists will look forward with 

 eagerness to the publication in full of his work upon that tract. 



But the area had its own ice, and while touching upon 

 glaciation, I may digress for a moment to call attention to 

 one promising hne of enquiry. The question of interglacial 

 periods is a vexed one, and so eminent a geologist as Lamplugh 

 from studies in this county, has maintained that there was 

 one period and one only of glaciation. Here he seems to be 

 opposed to the general opinion of geologists at home and abroad. 

 The work of Tarr in the Finger Lake Region of the United 

 States indicated the importance of erosional phenomena as 

 well as of those of accumulation as bearing upon this matter, 

 and he brought forward evidence in that area of an interglacial 

 epoch. In so doing, he called attention to the importance of 

 the simple geological structure of the region in facilitating 

 enquiry. We are deaUng with a similarly simple tract, and I 

 think the question may be settled here. Let me mention one 

 bit of evidence. Chapel-le-dale is a simple valley, which 

 seems to owe its general outUne finally to glacial erosion ; 

 nevertheless, since that outline was produced, water-t-rosion 



Naturalist 



