A. Sirahaii's Address to Section C, Geology. 451 



and plain present in varying degree proof that sheets of sedimentary 

 material originally horizontal are now folded and fractured. But 

 after a momentary interest aroused by some example more striking 

 than usual, glimpsed, it may be, from a train- window, the subject is 

 probably dismissed with an impression that such phenomena are due 

 to cataclysms of a past geological age and have little concern for the 

 present inhabitants of the globe. These stupendous disturbances, it 

 might be argued, can only have taken place under conditions 

 different from those which prevail now. We are familiar with 

 mountain-ranges in which their effects are conspicuous ; we have 

 carried railways over or through them and have been troubled by no 

 ■cataclysmic movements of the strata. Apparently the rocks have 

 been fixed in their plicated condition, and are liable to no further 

 disturbance. Parts of the world, it is true, are subject to earth- 

 quakes accompanied by Assuring and slight displacement of the 

 crust, but not even in earthquake regions can we point to an example 

 of such thrusting and folding of the strata being actually in progress 

 as have taken place in the past. Nor, again, can volcanic activity 

 be appealed to, for some of the most highly disturbed regions are 

 <3evoid of igneous rocks. Volcanic eruptions are more probably the 

 effect than the cause of the disturbances of the crust. Nowhere in 

 the world therefore, it will be said, can we see strata undergoing 

 such violent treatment as they have experienced in the past. How, 

 then, can we dispute the inference that the forces by which the 

 folding was produced have ceased to operate ? 



Before accepting a conclusion which would amount to admitting 

 that the globe is moribund and that the forces by which land has 

 been differentiated from sea have ceased to act, we shall do well to 

 look more closely into the history of the earth-movements to which 

 any particular region has been subjected. The investigation is one 

 which calls for the most intimate knowledge of the geological 

 structure, and, as time will admit of my dealing with a small area 

 only, I shall confine my observations to England and Wales, 

 •selecting such facts as have been established beyond dispute. 



At the outset of the investigation we find reason to conclude that 

 the movements, so far as any one region is concerned, have been 

 intermittent. Evidence of this fact is furnished wherever any 

 considerable part of the geological column is laid open to view. 

 Sheets of sediment, aggregating perhaps thousands of feet in 

 thickness, have been laid down in conformable sequence, all bearing 

 evidence of having been deposited in shallow seas. The inference is 

 inevitable that that period of sedimentation was a period of 

 uninterrupted subsidence. But sooner or later every such period 

 came to an end. Compression and upheaval took the place of 

 subsidence, and the strata lately deposited were plicated and brought 

 within the reach of denudation. Illustrations of the recurrence 

 of these movements abound, and I need dwell no further upon them 

 than to remark that movements of subsidence and upheaval may 

 be seen to have alternated wherever opportunity is afforded for 

 observation. 



