440 Maiv — On Subaerial and Marine Denudation. 



a few furtlier observations on some of the more salient points in 

 wliich Mr. Mackintosli differs from the advocates of subaerial denuda- 

 tion. Let me, however, in the first place, admit with him the full belief 

 by subaerialists in the existence of -numerous evidences of the coast 

 action of the sea over the land surface. The most superficial observer 

 must at once detect in the drift-covered surface and terraced outlines 

 of mvich of the drj' land, the existence of former progressive coast lines 

 of sea erosion over almost the entire surface ; indeed, it is this very 

 palpable evidence of the tooth of the sea on the land and its strongly 

 marked character, by which the advocates of subaerial denudation 

 believe they can distinguish between the work of the sea and the de- 

 nudation performed by rains and rivers, and that the surface erosion 

 performed by the sea has been so trifling as to scarcely interfere with 

 the general structure of surface brought about by subaerial agency. 



Valley Excavation produced hy Marine Currents directly assailing 

 the Coast (?). — The assumption that coast indentations and valleys 

 may be the result of marine currents directly assailing the coast, 

 though easUy disprovable in principle, is also capable of being tested 

 by the facts of the cases brought forward in illustration. The ad- 

 vocates of subaerial denudation hold that marine inlets and valleys 

 running up from the coast are the result of the submergence of 

 land previously moulded by rain and river action, and believe 

 that small local currents, having the power to perform the work 

 attributed to them, and the persistency to perform it on a parti- 

 cular spot, could never have existed. In long narrow channels, 

 such as the fjords of Norway, it is not unusual to find two nar- 

 row inlets opening out of the main channel exactly opposite each 

 other, implying on the marine theory of excavation, the existence 

 of currents striking from the same point in exactly opposite 

 directions. A glance at the map will at once show that the 

 Norwegian inlets are merely the seaward prolongation of valleys 

 that have their origin close to the Scandinavian watershed. If, as 

 I shall presently endeavour to show, the sea does no material work 

 below the tidal range, and that the excavation must therefore have 

 been done on its coast outline, how are we to account for the per- 

 sistency of points of resistance and points of erosion (and these 

 quite independent of the structure of the rock) on the line of the 

 fjords and their valley prolongations through such an immense 

 range of altitude ? Is it not obvious that the complete change of 

 coast outline involved in such an oscillation of level must have 

 repeatedly changed and disarranged the course of such assumed local 

 currents ? It is a very suggestive fact that this singularly indented 

 coast is now undergoing a change of level — may it not be recovering 

 itself from a submergence which caused the sea to run up the valleys 

 that were cut out by subaerial action on a land surface of greater 

 elevation than the present ? 



Along the indented west coast of Ireland it is well known that 

 currents do not directly assail the coast, but that the Gulf Stream 

 here takes a grand sweep to the N.E. almost parallel with it. 



In the case of the Aber valley, cited by Mr. Mackintosh as an ex- 



