Dr. J. W. Spencer — The Submerged Platform of W. Europe. 17 



Irrespective of the origin of the tablelands, whether the result of 

 stupendous faultings or of more gentle bulgiugs of the earth's crust, 

 with the frontal margins fashioned by waves, or by both, or by other 

 causes, the only point for consideration is the fact that the surfaces 

 of these slopes have been moulded by the action of rains and 

 streams, so as to be dissected by great deep valleys crossing all 

 the formations, since they were last elevated above the sea. Besides 

 many large valleys heading abruptly in the tableland, there are 

 numerous short tributaries, called in America by the name of 

 ' amphitheatres,' from two to ten miles long and thousands of feet 

 deep. These begin abruptly in the edge of the high plateaux, and 

 may be likened to gigantic wash-outs, such as are formed by the action 

 of rains upon the soft materials of an elevated coast, and elsewhere. 

 The elevation of the tablelands appears to have been interrupted 

 by pauses allowing for the formation of base-levels of erosion or 

 platforms or steps along the face of the great slopes and in the 

 valleys themselves. Such features upon the edge of the high 

 plateaux show the subaerial sculpturing of the great declivities 

 regardless of the primary origin of the slopes. Then comes the 

 important point that they are an exact representation, upon the 

 surface of the land, of the submarine valleys and amphitheatres 

 dissecting the slopes which descend from the submarine plateaux 

 to the ocean floors. If the form and gradients of the sculptured 

 features of the great terrestrial slopes, whether above or below 

 the sea-level, be carefully studied, they will answer for themselves 

 Mr. Jukes-Browne's remark "how the existence of river-made 

 valleys can possibly prove the declivity to have been made by 

 subaerial agencies passes my [Mr. Jukes-Browne's] comprehension"; 

 for Professor Hull is only considering the formation of such surface 

 features, when found beneath the sea, as evidence of changes of 

 level subsequent to the subaerial sculpturing of the platforms and 

 declivities themselves. 



Nor is it alone on the margins of the plateaux overlooking the 

 Gulf of Mexico that perfect topographic features similar to the 

 drowned valleys are to be found. The Grand Canon of the 

 Colorado is over 200 miles long, and reaches to a breadth of 

 thirteen miles and a depth of over 6,000 feet. It dissects a plateau 

 having a height of over 8,000 feet above the sea. There is no lack 

 of examples confirming the complete resemblances between the 

 erosion features of the bold reliefs of the land and those beneath 

 the surface of the oceans. The problem is one of great magnitude, 

 and the amount of the material available is not small ; but the 

 conditions for investigations from the simpler to the more complex 

 forms are more favourable in America than in Europe, and this is 

 no doubt why geomorphic studies have not received the attention 

 they deserve in Europe. The phenomena by which the geomorphist 

 reads the history of the land features seem so simple that some 

 geologists attempt to criticize the long and tedious investigations 

 of physical geologists without having studied the grammar of the 

 investigations. The result is precisely the same as would be the 



DECADE IV. VOL. VI. — NO. I. 2 



