FORM OF THE CONTINENTS— WATTS 201 



The "nappes" of rock, cut off from their origin ajid sliding for 

 dozens of miles, are a constant source of Avonder to all who have 

 considered the mechanics of mountain fonnation. They are so thin 

 as compared with their great length and breadth, that it seems im- 

 possible to imagine them moved by any force other than one which 

 would make itself felt throughout their every particle. Such a force 

 is gravitation, and it is of interest that some Alpine geologists and 

 Dr. Harold Jeffreys have used it in exj^lanation of them. Professor 

 Daly has also adopted gravitation on an even greater scale in his 

 theory of continental sliding; and one cannot fail to notice the in- 

 creasing use of the term "crust-creej^" by those working on earth 

 movement. 



Is there no other force comparable in its method of action to gravi- 

 tation but capable of producing movement of the earth crust in a 

 direction other than downhill ? Is it not possible, for instance, that 

 the tidal influence of the moon and sun, which is producing so much 

 distortion of the solid earth that the ocean tides are less than they 

 would be otherwise, and, dragging always in one direction is slowing 

 down the earth's rotation, may exert permanent distorting influence 

 on the solid earth itself? May it not be that such a stress, if not suffi- 

 ciently powerful to produce the greater displacements of continental 

 drift and mountain building, may yet take advantage of structures 

 of weakness produced by other causes, and itself contribute to the 

 formation of nappes and to other movements of a nature at present 

 unexplained ? 



Our knowledge of geology has been gained by the survey of the 

 rocks, the study of their structures, and the delineation of both upon 

 maps and sections. This work is being accomplished by geologists 

 all over the world, and this country and its dependencies have con- 

 tributed their full share. It is therefore opportune to note that there 

 has just been celebrated the centenary of the Geological Survey of 

 Britain and, with it, the opening of the new Geological Museum at 

 South Kensington. 



A century ago H. T. de la Beche, one of the devoted band of 

 pioneer workers then studying the geology of the country, offered to 

 "affix geological colours to the new maps of Devon and Cornwall" then 

 in course of issue by the Ordnance Survey. His offer was accepted, 

 and, at his own expense and on his own feet, he carried out a geolog- 

 ical survey of some 4,000 square miles. In 1835 he was appointed 

 to continue this task, with a small salary and a few assistants. Thus 

 was started the first official geological survey, an example widely 

 followed by other nations and dominions. De la Beche's conception 

 included also a museum of economic and practical geolog}', a library, 

 a record of mines, for which he secured support from a strong com- 



