Correspondence. 575 



are now exciting in Britain, Ireland, and Scandinavia, I lose no 

 time in sending you the above rough sketches.^ 



D. Mackintosh. 



Taunton. 



P.S. — I see the Eev. 0. Fisher, in your last number, has arrived 

 at a conclusion in support of which I have been collecting facts 

 during the last eighteen months, namely, that the superficial angular 

 debris, earth, and loam, from which our slopes and hills partly 

 derive their smooth and rounded forms, is not principally a dis- 

 integration in situ, but has been carried or driven along by a simulta- 

 neously wide-spread agency. 



MARINE DENUDATION AND TIDAL CURRENTS. 

 To the Editor of the Geological Magazine. 



SiE, — Without wishing to unduly prolong the discussion on this 

 subject, which has recently occupied so much of your space, may I 

 briefly notice a point in the letter of my friend, Mr, Mackintosh, in 

 which, I think, he seems to reverse the order of cause and effect ? 

 Admitting the influence which the form of the coast-line has on the 

 direction and localization of tidal currents, the difficulty on the 

 marine theory, still remains unexplained, as to the original excavation 

 of these inlets and channels, before they could determine the direc- 

 tion of the eroding sea-line. 



The phenomena exhibited in shallow seas in the constant shifting 

 of sand- and mud-banks, and the ploughing up and re-deposition of 

 matter, such as is now going on in the German Ocean, and is so well 

 exemplified in both the internal structure and surface-contour of 

 much of the marine drift, seem to afford the strongest evidence of 

 the changeable character and want of local persistency of small 

 marine currents. 



As regards deep seas, the difficulty in accounting for the marine 

 excavation of continuous valleys, may be briefly stated thus : If the 

 whole was done simultaneously, it would involve — in the case of 

 many of the Swiss valleys — (having a range of altitude of 7000 or 

 8000 feet) — a depth of action far beyond what is known to be the 

 lower limit of marine currents ; and if progressively by coast action, 

 a persistency of position which seems incompatible with the entu'O 

 change of contour during emergence or submergence, to an extent 

 equal to the range of altitude of the valley. 



A friend, who has recently been in Norway, informs me that the 

 Fjords invariably terminate in a valley ; admitting that the cliff-girt 

 sides of the Fjords are the result of marine erosion, does it not seem 

 more probable that this was superadded to a previously existing 

 subaerial valley, than that the junction of the Fjord with the valley 

 prolongation was a matter of accidental coincidence? And if the 



^ Fig. 2 is Tery regularly grooved, and the whole surface smoothed. 



