312 TYNEDALE ESCARPMENTS; 



than a runlet, has been equal to the task of keeping the beds to 

 the left of it well scarped, and as the sandstone is set ojff by a 

 thick shale beneath it, and cleared above into a long dipslope by 

 A, this escarpment is now the most imposing of the series. Yet 

 its sandstone is not the thickest, and it will be noted that the 

 thinnest sandstone of the group, that underneath B, has formed 

 a distinct platform, compared with the ledge to which circum- 

 stances have limited the massive bed further to the right. 



In these advanced stages of devolpment it is important to gain 

 a correct idea of the changes to be noticed in passing from the 

 mouth to the source of a large transverse stream. The diagram 

 will give an idea of this if all the gradations of the four streams, 

 A, C, D, E, are traced in succession. At first we note the escarp- 

 ments gathered up into terraces in the bank, but as we rise with 

 the lessening stream their dipslopes lengthen, they open out, and 

 take the escai-pmental form. 



2. Development hi/ Atmospheric Disintegratioyi alone. — If we 

 keep strictly to the diagram, however, we ought, in thus ascending, 

 to reach the initial stage of the runlet E, where no escarpment 

 exists at all. But here will come in the influence of atmospheric 

 waste pui*e and simple, to which, in the nature of the case, we 

 are now restricted. It is obvious that in the advanced stages at 

 which the ridges in the lower ground tend to become terraces, 

 increasingly liable, as is evident from the development of the 

 channel A, to entire obscuration, we may expect to find upon 

 the watersheds escarpments of the completest tyjic. Frosts and 

 ruins have been quietly working there for a greatly prolonged 

 period, and if they have power to chisel out the structuii', es- 

 carpments must be the ineWtable result. 



Ere this stage can be attained, however, the longitudinal valley 

 may be expected to possess the chai*acteristics of great age. In 

 following out such parallelism as may exist between the escia-p- 

 mcntal development as we actually find it and the foregoing hy- 

 pothetical case, it is well first to look at the valleys. 



Ti/nedale Valleyn. 1 . Lonyitudiual. — The vales of North and 

 South Tyne arc both, in the main, greatly widened, although not 



