TRANSACTIONS OF SECTION E. 427 



Through this plateau hoth the Don and its tributary the Went, flowing in a 

 parallel course to the north, have to force their way. The rivers flow through nar- 

 row valleys of fertile pasture bordered by undulating wooded banks, and the 

 western escarpment, in the Went valley, is bold and picturesque. Leaving this 

 region at Hexthorpe, the Don enters a level plain which, beyond Doncaster, is in 

 places overlaid with peat, and there are wide stretches of marsh-lands called carrs ; 

 a vast level extending to the Humber. 



Such are the general features of the Don river-basin, which would strike the 

 least observant traveller. But the physical geographer investigates and explains 

 the occurrence of these features. He inquires why the western hills are the 

 loftiest and most craggy ; why the Don changes its course and flows in a deep 

 trough along their skirts ; why the adjoining country, though still hilly, is softer 

 in outline. He examines into the reason of the existence of a belt of plateau land 

 through which the Don and Went have to pass in scarped ravines ; and into the 

 causes which have led to the formation of the vast levels extending from Don- 

 caster to the Humber. In these researches, our science receives aid from geology, 

 which tells us the nature of the various rocks and the influence they have on the vary- 

 ing features of the earth's surface as we now see it. We do not concern ourselves with 

 the way in which the rocks were originally formed, with lists of fossils with long 

 Latinized names, or with the condition of the earth's surface in the remote ages when 

 those fossils were living creatures. We are only interested to know the nature 

 and texture of the rocks as they now exist, the order of their deposition, and 

 their economic uses. This information teaches us the causes which have produced 

 the varied configuration of the surface as we now see it. 



Geology tells us the story of the formation of the Penine range of mountains 

 where the Don and its tributaries have their sources. The disturbances which the 

 beds of rock have undergone have had the effect of crumpling them up into a 

 number of troughs and arches. As each arch was raised up, the denudation took 

 slice after slice off its crest, so that along the saddle of each anticlinal line the 

 lower beds were laid bare, and now appear on the surface. The Pennine anti- 

 clinal, of which the hills containing the sources of the Don form a part, is a broad 

 arch extending north and south from Scotland to Derbyshire. Along the central 

 line of this arch, in the part whence flow the Don sources, the hard massive sand- 

 stones of the millstone-grit come out and, on account of their hardness, stand up 

 in a chain of rugged and lofty hills and moorland plateaux. It is the hardness of 

 the rock in the millstone-grit formation which produces the strongly featured 

 country of this part of the Penine range, and, by offering greater resistance to 

 denudation, maintains the superior height of these hills over all the country on 

 both sides. 



Where the Don makes its great southerly bend from Penistone to Sheffield the 

 surface formation has changed, its course is then over the lower coal measures and 

 skirting the edge of the millstone-grit. In this fact, no doubt, is to be found the 

 reason of the direction taken by the river. The country where the lower coal 

 measures form the surface shows a repetition of the features of the millstone- 

 grit region, but somewhat less marked, and with less elevation. 



On leaving Sheffield, the Don changes its course and enters the country of the 

 middle coal measures, where the bold features which characterise the lower coal 

 measures and the millstone-grit are missing. Here again there are indications of 

 the causes which decided the direction of the river bed. There are two faults 

 ranging in a north-east direction from Sheffield, along either side of the valley of 

 the Don, towards Oonisborough, and between these faults the rocks are much con- 

 torted. The southerly Don fault passes S.W. to N.E. through Sheffield, along the 

 south-east margin of the Don valley to near Aldwark, and runs on by Thrybergh 

 and Hooton Roberts to Cadeby. The thick beds of sandstone which alternate 

 with the coal in this formation often form bold escarpments, such as the ridge 

 which adds so much to the beauty of Wentworth Park. 



We can next account for the picturesque ravines through which the Don and 

 Went find their way before reaching the levels. For here is the more recent 

 Permian formation of magnesian limestone which extends in a narrow belt, four or 



