564 Professor J. W, Spencer — Reply to 3fr. Hudleston — 



borne in mind that the locations are not accurate, and that in off- 

 shore hydrography, errors of location up to five miles are 

 permissible (though usually much less) even in good work, when 

 the soundings are made at different times. Consequently, the 

 Avindings of the valleys are only approximately located, and there 

 may even appear interruptions, but their deptlis at various points 

 are correct. Under all these conditions, I am forced to give value 

 to the intermediate soundings passed over by Mr. Hudleston, and 

 reach only one conclusion, which is Professor Hull's — that the Fosse 

 de Cap Breton is a continuous valley to beyond the depth of 1,500 

 fathoms, and from the character of the steep sides it appears to 

 partake of the nature of a caiion. From the soundings, the floor 

 of the fosse, as thus extended, seem to be characterized by three 

 steps, separated by long intervals where the slope is reduced to 

 a few feet per mile, while the mean declivity of the intervening 

 steps is 200 feet per mile. If fuller soundings were made, the 

 steps might be found more abrupt, and there might be a larger 

 number revealed. Mr. Hudleston's explanation of the 1,500-fathom 

 sounding as being a " hole rather than a channel " — an expression 

 used similarly elsewhere — would appear to be a refuge from the 

 valley hypothesis, unless it is shown how such are formed, especially 

 when there is a succession of them.^ 



I wish to correct a criticism. He says, " that Professor Spencer, 

 having long studied the Caribbean Sea — perhaps the most unstable 

 region of the earth — appears to have an exaggerated notion as to 

 epeirogenic uplifts on both sides of the Atlantic " ; and he further 

 objects to the hypothesis that the Eockall embayment, west of 

 Ireland, has been fashioned by atmospheric agents, and suggests 

 that both it and the Lightning channels, and the deeps of the 

 Norwegian Atlantic were due to tectonic causes. Whatever were 

 the causes of the basin, the claims of Professor Hull and myself 

 are only that the barriers were once land, which were moulded by 

 atmospheric agents, producing the valleys dissecting them. 



I fear that my critic's impression of the instability of the Caribbean 

 region is very much magnified. It is now certainly established that 

 the principal changes of level, since the early Tertiary period, over 

 that region — vastly larger than the Norwegian basin — have occurred 

 with remarkable persistency, though varied in magnitude. And 

 these changes have extended to the North American continent, and 

 continued northward to regions considered the most stable. I suspect 

 that the most of these changes are represented in the eastern Atlantic, 

 which the evidence brought out indicates. At no time have I stated 

 that the same individual oscillations extended to both sides of the 

 Atlantic, as the oscillations may not prove to have been absolutely 

 synchronous. They may yet be found to have alternated. The 

 changes may also have been more complete in one region than 

 another. 



^ For a restoration of this submerged river cliannel as determined by Prof. Hull, 

 see Geogr. Joura. for March, 1899, with map. 



