Mevietvs — Life of Sir Joseph Preslioich. 375 



valleys bave been mainly eroded by the rivers wbicb still flow in 

 them. Though this explanation of river-valleys was strongly 

 insisted upon by Hutton and Playfair, and had been demonstrated 

 for Central France by Desmarest and afterwards by Scrope and 

 Lyell, it had never attained wide acceptance among geologists. 

 When it was adopted and enforced by Prestwich on a basis of well- 

 ascertained fact, it came almost with the freshness of a new dis- 

 covei'y. He quickly saw its significance in regard to the slow 

 sculpture of the face of the land, and the great antiquity which it 

 proved for the older and higher terraces of gravel. In his memoir 

 read before the Royal Society in 1862, he dwelt on the evidence that 

 could be adduced of powerful and long-continued, erosion in the 

 valleys by the streams that still flow in them ; and he continued 

 to bring forward additional proofs in support of his views, until 

 geologists everywhere admitted the validity of his reasoning. 

 There remained, indeed, differences of opinion as to the intensity 

 of the operations by which the denudation had been effected. The 

 followers of Lyell would not admit that the observed facts demanded 

 the existence of larger rivers and more powerful floods than might 

 be witnessed at the present time, while Prestwich was always 

 prepared to find that the geological agents had worked on a grander 

 scale in former times than they do now. But the fundamental fact, 

 that the valleys of the south-east of England and the north-west of 

 France had been carved out by the action of the rivers that drain 

 them, was now accepted without further demur." 



" To Prestwich, therefore, must be assigned a not inconsiderable 

 share in promoting the advance made during the last thirty years 

 in the investigation of the history of terrestrial topography. He 

 continued to interest himself in the subject up to the end of his life. 

 Some of his last contributions to science dealt with the carving out 

 of the river - valleys around his home at Shorehara and in the 

 neighbouring district of the Weald." (p. 404:.) 



" It is interesting to note that Prestwich began his geological 

 career by studying in minute and patient detail the coalfield of 

 Coalbrookdale, and that he was thereafter led to explore the Old 

 Red Sandstone of the Moray Firth. This early work was so eclipsed 

 by the brilliance of his later researches among much younger 

 formations, that a later generation of his contemporaries hardly 

 realized the rare excellence and originality of his first great essay. 

 The elaborate memoir on Coalbrookdale, presented to the Geological 

 Society when its author was only a young man of twenty, is certainly 

 a remarkable performance. Those to whom it was first addressed 

 can hardly have failed to recognize in its author one of the future 

 leaders of English geology. Selecting an area of about one hundi-ed 

 square miles, he carefully mapped its geology on a scale of one inck 

 to a mile. The map was no mere sketch, but an elaborate survey, 

 wherein the outcrops of the several seams of coal were traced, and 

 the positions and effects of all the principal dislocations were 

 represented. The structure of the ground was further displayed in 

 a series of horizontal and vertical sections, while additional details 



