THE ORIGIN OF MOUNTAINS. 31 



times the movements of the earth's crust must have been greater in 

 extent and rapidity than they now are. 



In conclusion I would add a few reflections which a trip from 

 Norwich to the Lake Mountains afforded in the summer of 1878. To 

 one whose time is mainly devoted to geological questions a holiday 

 trip should be a change, not only of scene and air, but of work. And I 

 must confess to feeling little inclined for minute observations, caring 

 not much whether a rock of quartz-trachyte came up here or a Tetra- 

 grapsus was found there. It was sufficient to know, from the laborious 

 observations of others, that the mountains told a tale of gradual 

 formation ; that the slates of Skiddaw, the oldest rocks in the district, 

 were at one time the soft muds of a primeval ocean, in which traces of 

 life then occurred in the shape of mollusca (brachiopoda) and Crustacea 

 (trilobites,) with tracks of worms and ripple marks ; how succeeding 

 the deposit of ten thousand feet of these materials volcanic action 

 became intense ; and that in the green slates of Borrowdale (of whioh 

 many of the houses are chiefly built) we have at first submarine volcanic 

 deposits, then ashes and lava-flows ejected on land. The late Mr. 

 Clifton Ward has told us that the boss of Castle Head, Keswick, was 

 probably the original centre of intense volcanic action, the stump, in 

 fact, of an old^volcano. Some twelve thousand feet of this Borrowdale 

 series remain to tell the tale, and being differently acted upon by the 

 weather from the Skiddaw slates, they form the rough hills in Borrow- 

 dale and near Grasmere, distinct from the smoother outlines of the 

 more truly slaty hills of Skiddaw. 



These rocks were upheaved and considerably denuded before the 

 succeeding Silurian rocks of Coniston and Windermere were laid down, 

 comprising fourteen thousand feet more of strata. And these beds 

 were subsequently rolled and disturbed so as to form a mountain group 

 as early as Carboniferous times, before our coal was formed. Thence 

 and in succeeding periods they have been up and down, but not to any 

 great extent disturbed. The conformation of the strata has remained 

 much as it is now, but the various agents of denudation, sea, rain, and 

 rivers have at intervals laboured in carving out the main features now 

 represented, while in the " Great Ice Age," not only was much denuda- 

 tion effected, but many scattered boulders were distributed over the 

 surface, which here and there was scored or smoothed by the passage 

 of the ice and its embedded stones. 



In remembering the old volcanic eruptions of Keswick, we must 

 bear in mind that even the volcanic deposits themselves have been 

 disturbed, bent, and fractured. 



Snowdon, too, is composed partly of aqueous and partly of igneous 

 rocks crumpled together, out of which the present mountain has 

 been carved, with no direct reference to the volcanic features that 

 formerly affected the area. In the Alps, too, according to Professor 

 Heim, all the eruptive rocks are much older than the elevation of the 

 chain, which proves that they have merely played a passive part, like 

 the sedimentary rocks themselves, during the elevation.* 



* Geol. Mag., Dec. 2, vol. vi., p. 131. 



