494 TRANSACTIONS OF SECTION E. 



dale which continues the general direction of the Upper Tees and is approxi- 

 mately the chord of the great southward bend of the middle Tees. In the 

 Staindrop Plains, an area of marsh finally reclaimed only a century ago, the 

 beck is diverted southward to the Tees through a valley which is much narrower 

 and younger than Langleydale. The main valley is continued eastward and 

 occupied in turn by the Langton and Cocker Becks before it is merged in the 

 lowland. This northern west-to-east valley is very similar to the one south of 

 the Tees which is occupied by the River Greta and the Tutta and Clow Becks. 

 These valleys contain many examples of the early effects of human interference 

 with stream development. 



There are thu.s in ]\Iiddle Teesdale two piincipal west-to-ea.st valley lines. 

 The development of these valleys, the subsequent union of their water.s in the 

 Tees, which flows between them in a much younger valley, and the absoriJtiou 

 of the smaller streams into this river system explain the great width of Tees- 

 dale in comparison with the neighbouring dales and the chief peculiarities of its 

 streams. The direction of the consequent streams is a few degrees north of 

 east, with a tendency to convergence from north and south due to the greater 

 elevation of the Cross Fell and Ingleborough domes. The Tees crosses the con- 

 sequent valleys, along a line determined mainly by fault-lines in the strata, and 

 has thus become the master stream. 



Except for the part.s of streams in fault-line valleys and in subsequent 

 reaches due to stream capture, there are few subsequent, and still fewer obse- 

 quent, streams; hence tlie river system as a whole is iu a comparatively early 

 stage of development. It is, however, the product of at least three distinct 

 cycles of erosion : 



1st. The comparatively smooth surface of the upland is part of a i>enciilain. 

 If its valleys were filled up it would be a plain sloping gently eastward, 

 with its surface cutting across the rock strata at a small angle. The 

 formation of this peneplain probably occurred during the Tertiary era. 

 2ik1. The wide shallow mature valleys mark the second cycle. Their shallow- 

 ness indicates that the change of base level which caused their formation 

 was small ; and their relation to the glacial drift and the route of the ice 

 indicates that they had reached their full development before the Ici; 

 Age. The elevation which led to their formation probably occurred in 

 the latter part of Tertiary time. The main consequent valleys are all of 

 this type ; and the more imjiortant of the subsequent valleys are also 

 ))re-glacial, though somewhat younger. The Ice Age does not seem to 

 iiave caused any serious changes in the stream lines of Teesdale ; but the 

 extensive river terraces of many of the valleys probably date from the 

 period following the melting of the ice. 

 3rd. Tlie deep and narrow gorges in which many of the streams flow are the 

 product of the last cycle of development, wliich is still in a very youth- 

 ful stage. Its initiation was due to a post-glacial uplift of the region. 



The change from the second to the third cycle is readily seen in the longi- 

 tudinal sections of the streams, most of which show very marked changes of 

 slope. The fall is usually much greater in the lower course than in the middle. 

 A typical tributary valley consi.sts of three clearly marked sections. First, the 

 upper course on the upland with a very slight valley. Second, a broad and 

 shallow valley on the floor of which the stream meanders. Thiid, a gorge in 

 the bottom of this wide valley in which the stream rushes along over a series of 

 rapids. These three sections of the valley repeat the three types of to])o- 

 graphy wliich characterise the district as a whole, and are tlie results of the 

 three cycles of erosion to which its present form is due. 



Some Considerations on Former Movements and Distribution of 

 Pointlation in South Britain, and its Infl.uences. By Professor 

 TT. J. Fr.EURR. 



5. The Study of Cities. 

 By Professor Patrick Geddes and Miss M. Barker. 



