568 Correspondence. 



ence is there made in the Popit/ar Science Beview (for October, 1866), 

 which he was bound to do before he undertook to give an exposition 

 of my opinions, he would scarcely have represented me as being 

 " a believer in the sea, and nothing but the sea" as an agent of denu- 

 dation. So far from this being the fact, I state in the former paper, 

 with regard to the scooping out of the valleys of the Lancashire 

 Hills, that they have been formed by rivers " in the great majority 

 of instances" (page 474:), and again (in page 477), I add, "the 

 more I consider this subject, the more 1 am satisfied, that in the 

 great majority of instances in this region, the extent and limits of 

 river action are capable of the clearest demonstration. Most of the 

 valleys are really double valleys, the smaller being alone due to 

 river denudation," and the evidence of this lies in the fact — that the 

 larger, or primary, valleys are filled with terraces of Marine Boulder- 

 clay, and are really plains of marine denudation in their earlier 

 stages. 



In the paper in the Popular Science Beview, I adopt a two-fold 

 view of denudation, mider the heads of " Vertical Denudation," and 

 " Horizontal Denudation ;" the former term including the formation 

 of " channels and furrows, either branching or lying along parallel 

 lines, as in the case of mountain chains," by the action of frost, rains, 

 rivers, and glaciers. Under the term. " horizontal" denudation, I 

 include the formation of plains and terraces by wave action, either 

 of the sea, or large lakes. 



If my critic had glanced at the same paper he would also have 

 seen that I adopt, though with some hesitation, the views of Professor 

 Eamsay, Dr. Foster, and Mr. Topley, regarding the subaerial denu- 

 dation of the Weald ; and, without any hesitation, those of Mr. P. 

 Scrope regarding the formation of valleys and escarpments in the 

 region of Auvergne ; and after this statement I am quite ready to 

 leave it to the judgment of your readers whether or not I am to be 

 regarded as " a believer in the sea and nothing but the sea." 



A believer in the sea I certainly am ; both in its power of forming 

 valleys and escarpments, and this from the evidence of my own eyes. 

 I have seen along the coast of Cantyre, channels several hundred 

 feet in length, with steep walls scooped out of tough gneissose rock 

 by wave action, and caves hollowed out of porphyry and other 

 rocks, like part of a railway tunnel, many yards in length, and I 

 care for no a 2}riori arguments which are intended to prove that after 

 such exhibition of the power of wave action to cut narrow channels 

 in the rock, the formation of valleys by such an agent is an impos- 

 sibility. Knowing the variety of agencies which nature employs in 

 the formation of the features of the earth's surface, and believing 

 that each special district requires the application of special principles, 

 I altogether repudiate as of universal application some of the general 

 axioms laid down by Mr. Whitaker with such show of authority ; 

 knowing from ray own experience that some of them are contrary 

 to fact. I shall just remark on one or two of them here. He says : 



(1) " Escarpments always run along the strike, whilst sea-cliffs 

 rarely do so." The "rarely" is a saving clause, as there are many 



