1889.J on the Highlands of Scotland and the West of Ireland. 538 



the north-west of Europe. Doubtless, each of the subterranean dis- 

 turbances more or less affected the surface. The land was by degrees 

 ridged up above the sea, and its height and breadth were j^robably 

 from time to time increased by local uplifts accompanying the 

 disturbances. But as soon as the land aj)peared, it began to be 

 attacked by the waves, the air, rain, and running water. Terrestrial 

 convulsions were intermittent, but superficial waste continued uninter- 

 rupted. Whatever may have been the character of its topography, 

 the first formed land, as soon as it rose, became a prey to the denuding 

 forces, and had its original surface gradually stripped off. We 

 have no means of telling how great a thickness of material was in 

 this manner removed from the land before the time of the next geo- 

 logical period, nor for how vast a time this slow process of denuda- 

 tion went on. All that we can now discover is a series of detached 

 fragments of the surface of this primeval Europe, which have been 

 preserved by being buried under the pile of material formed out of 

 the waste of the Archaean rocks. From these fragments we learn that 

 the rocks had been enormously denuded so as to lay bare to the surface 

 some of their deep-seated parts, the land shaped out of them having 

 been carved into dome-shaped hills and basin-like hollows, not very 

 different from those which are so characteristic of the Archaean 

 tracts to-day. 



II. The Cambrian Period. 



We now reach the base of the stratified formations of the British 

 Isles, and enter upon a series of records which deal not with subter- 

 ranean but with superficial changes, and in which the earliest 

 geographical conditions of our area are more or less fully chronicled. 

 These records consist of a pile of dull-red sandstones, conglomerates, 

 and breccias, with grey, green, and black mudstones, marls and 

 shales, attaining a maximum thickness of perhaps 10,000 feet. 

 This great accumulation, chiefly of coarse sediment, was derived from 

 the w^aste of the Archaean land. The pebbles in its conglomerates are 

 fragments of that land, and enable us to form some conjecture as to 

 the nature of the materials that composed its surface. An examina- 

 tion of these pebbles brings to light the important fact that besides 

 the detritus of the gneiss and other Archaean rocks which can now 

 be seen in situ, the conglomerates are made up of materials derived 

 from some still older sedimentary formations which have entirely 

 disappeared from our area. These included such rocks as quartzite, 

 greywacke, shale, and limestone, besides abundant pieces from the 

 lavas, which I have already referred to as having probably been 

 erupted to the surface in pre-Cambrian time. The destruction of 

 these intervening deposits, and the chance discovery that they once 

 existed because fragments of them have been found in later con- 

 glomerates, serve to impress upon us the imperfection of the 

 Geological Record and the vastness of the intervals of time which 

 may sometimes separate two successive groups of rock. 



