276 SCIENCE PROGRESS. 



stream courses which were initiated in a geological sense 

 simultaneously, and it is of importance to determine to 

 which of these causes the complexity of the drainage system 

 of Britain is due. It is generally conceded that the rivers 

 which flow over considerable parts of Eastern England were 

 initiated in Miocene times, or at any rate during the system 

 of earth-movements which culminated in parts of Europe in 

 the Miocene period, consequently, if our whole river drain- 

 age was established simultaneously, it must be referred to 

 this date ; whereas, if drainage systems were developed in 

 our island at different times some of these must be anterior 

 to Miocene times. It appears to be the opinion of most 

 geologists that the latter supposition is the true one, but it 

 does not seem to be founded upon anything beyond general 

 impressions; a traveller amongst the old rocks of the Scotch 

 Highlands, Cambria or Cumbria, is naturally impressed 

 with the antiquity of the rocks on which he treads, and is 

 unconsciously led to regard the area formed of those rocks 

 as one which has existed as dry land through long geolo- 

 gical times. It is desirable, therefore, that we should at the 

 outset consider how far the geological antiquity of portions 

 of our island as dry land is proved by the evidence at our 

 disposal. 



Every uplift, whether of sea-floor to form land or of pre- 

 existing land to a higher elevation, will tend to influence 

 the drainage and to produce watersheds or divides at first 

 coinciding with the point or line of maximum uplift, though 

 it depends upon the previous inclination of the uplifted 

 rocks whether, after uplift, any definite relationship can 

 be traced between anticlinal axes and watersheds. Now, 

 geologists are fairly agreed as to the periods at which the 

 rocks of the British Isles were affected by important uplifts ; 

 and those which require consideration in connection with 

 the subject under discussion occurred at the close of Lower 

 Palaeozoic times (mainly in Devonian times), at the close 

 of Upper Palaeozoic times (especially during the Permo- 

 Triassic period), in the middle of Cretaceous times, and in 

 Tertiary times (especially the Miocene period) we may 

 speak of them as the Devonian, Permian, Mid-Cretaceous 



