452 Notices of Memoirs — British Association — 



On extending our observations we are led to infer tliat tbe 

 movements of the crust were developed regionally, not universall}'. 

 The areas of subsidence, for example, evidenced by tlie marine 

 formations had their limits, though those limits did not coincide 

 with the shores of existing seas, nor has reason been found to 

 believe that the proportion of land to sea has varied greatly in 

 past times. The limits of the area affected by any one movement 

 of upheaval are more difficult to determine, but the effects were 

 manifested in the crumpling up of comparatively narrow belts of 

 country, and are easy of recognition. 



Further than this, we ascertain that the movements of one region 

 were not necessarily contemporaneous with those of adjoining 

 regions. The forces operating upon the crust of the eartb came 

 into activity in different places at different times, and, while some 

 Continental tracts have been but little disturbed from early geological 

 times, there are parts of the globe which have been the scene, so to 

 speak, of almost ceaseless strife. Among the latter we may include 

 the British Isles. 



These are commonplaces of geology, and I mention them merely 

 to emphasise the fact that the geological structure of these islands 

 is the result of movement superimposed upon movement. Obviously, 

 therefore, in order to gain a comprehensive view of the operations 

 which were in progress in any one region during any one epoch, we 

 have to find some means of distinguishing the movements of that 

 epoch and of eliminating all which preceded or followed it. This, 

 briefly, is the problem which has engaged the attention of geologists 

 for many years past, and upon which 1 propose to touch. 



The determination of the age of a disturbance is seldom easj', and 

 among the older Pa]a30zoic rocks is often impossible ; but at the 

 close of the Carboniferous period, during the great Continental 

 epoch which led to and followed upon the deposition of the Coal- 

 measures, there came into action a set of movements of elevation 

 and compression, which generally can be distinguished both from 

 those which preceded them and from those which have been super- 

 imposed upon them. The distinction depends upon the determination 

 of the age of the rocks affected by the movements. For example,, 

 a movement by which the latest Carboniferous rocks have been 

 tilted from their original horizontal position is obviously post- 

 Carboniferous. On the other hand, if Permian rocks lie undisturbed 

 upon those tilted Carboniferous rocks, it is equally obvious that the 

 movement was pre-Permian. Now it happens that earth-movements 

 of the date alluded to were particularly active in the British Isles, 

 and played an important part in shaping the platform on which tho 

 Permian and later rocks were laid down. Though they have been 

 more completely explored than others in the working of coal, their 

 further investigation is of the greatest economic importance. I have 

 attempted, therefore, briefly to sketch out the principal lines along 

 which earth-movements of that age came into operation in England, 

 premising, however, that by Permian I mean the Magnesiau Lime- 

 stone series, and not the " Permian of Salopian type," which is now 



