268 ORIGIN OF THE ROCKS AND SCENERY OF NORTH WALES. 



nearly the same level. A geological map of such a surface would not 

 differ materially from the present geological map, for the same rocks 

 would crop out in the same order. Out of such a surface we believe the 

 existing scenery to have been carved by the action of rain and streams, 

 frosts and glaciers, through many geological epochs. Three factors, then, 

 have to be considered in determining the origin of the existing scenery. 

 Firstly, the direction of the water courses as determined by the original form 

 of the ground ; secondly, the character of the rocks of which the country is 

 composed; and, thirdly, the time during which denudation has been in 

 operation, and the nature of the climate during that time. 



The due consideration of any one of these facts would require a 

 paper as long as the present one. I can, therefore, only call your atten- 

 tion to one or two points. No traveller in North Wales can fail to be 

 struck by the marked influence of rock structure on scenery. Many a 

 vertical precipice is seen to be due to the coincidence between the 

 direction of the valley and the direction of the joint planes in the rock; 

 and many a jagged ridge shows a continued repetition of similar outlines, 

 due also to the influence of joints. Then, stratification frequently 

 produces a characteristic appearance. When it is horizontal, or nearly 

 bo, it presents the appearance of cyclopean masonry in ruins. More 

 frequently it dips in a definite direction, and at a high angle, scoring the 

 face of the precipice with parallel lines ; occasionally, as in the frightful 

 precipice overhanging the dark and gloomy Llyn Llydau, it takes the 

 form of a series of graceful curves. On all sides we find abundant 

 evidence of the connection between rock structure and scenery. Indeed, 

 it is not too much to say that, just as the work of a sculptor is 

 determined as much by the character of the material in which he works 

 as by the tools he uses in fashioning it ; so the scenery of a country is 

 determined as muoh by the nature of the rocks that compose it as 

 by the denuding agents, the sculpturing tools of nature, that aot 

 upon it. 



In considering the third factor, time and climate, and its importance 

 in determining the scenery of North Wales, it is necessary to bear in 

 mind two facts. First, the time during which North Wales has been 

 subject to denudation is enormous. Off and on the denuding agents have 

 been at work since the Silurian period, for Cambrian* rocks occur as 

 fragments in Silurian deposits. Secondly, the climate during that time 

 has not been constant. Variations, both in the amount and in the nature 

 of the precipitation have taken place. Fortunately, we have at present 

 in the district, abundant proof of the truth of this latter statement, and 

 also of its importance as bearing on the origin of scenery. 



In the course of my rambles I have frequently had the opportunity 

 of noticing the effects of glacial action. I have seen them near the 

 termination of the Eosenlaui and Grindelwald glaciers, on the surface 

 of rocks that have only been exposed to the light of day by the retreat of 



* The term Camorian is used as Sedgwick proposed ; so that it includes the 

 Lower Silurian of many geologists. 



