190 Correspondence — Colonel George Greenwood, 



on the floor of the surrounding ocean, as is known to have been the 

 case with the Isle Julia, near Sicily, the Kaimenis in the crater of 

 Santorino, and other instances. 



Professors Eamsay and Geikie both bear witness to the large 

 proportion of the sedimentary strata of early geological ages within 

 the British Isles, that owe their origin to the fragmentary ejections 

 of submarine or insular volcanos, wholly independent of sub-aerial 

 denudations. So too Mr. Darwin, in his work on South America, 

 describes an immense geographical area east of the chain of the 

 Andes, as composed in great part of conglomerates alternating with 

 beds of lava, all ejected from submarine volcanos. 



These various sources of sedimentary accumulation at the bottom 

 of the ocean, if added together, may fairly be considered as pro- 

 ductive in the course of ages, of an aggregate mass of strata fully 

 equal to that derived from the contemporary denudation of the land; 

 and this, if admitted, would at the least double the figures in Mr. 

 CroU's estimates of the mean annual amount of sedimentary strata 

 produced by all causes combined. I should be the last of all 

 geologists to underrate the effects of sub-aerial denudation. But 

 it seems to me impossible to ignore the fact that immense accumu- 

 lations of sedimentary strata are, and have always been, in course 

 of production beneath the sea-level, by processes from which sub- 

 aerial agencies are wholly excluded. 



CoBHAM, March Uth, 1871. Gr- POULETT SOKOPE. 



TERRACES OF NORWAY. 



Sm, — Under this heading in your number for this month is a 

 notice of a work by Professor Kjerulf. The Professor's facts accord 

 exactly with the theory which I have had the honour to publish in 

 your pages (Geological Magazine, November, 1866^ p. 519, and 

 May, 1867, p, 1), and his theory would only differ from mine in 

 this, that he supposes the alluviums of which the terraces are the 

 remains to have been formed under a permanent "water-surface, 

 which caused the materials washed down by the streams to be heaped 

 up everywhere to the height marked out," p. 75 ; and I suppose them 

 to be formed by deposit on land from repeated temporary overflows 

 caused by rain or by melted snow which is frozen rain.^ No one 

 will dispute this as regards the marine alluvium of the Nile. It 

 stands above the surface of the sea, and rises now by deposit from 

 yearly overflow. But if the north of Africa were to rise ever so 

 gradually, it would cause the Nile to fall into the sea. That is, 

 directly as the rise of the land would be the fall of the river into the 

 sea. Directly as its fall into the sea would be its power of deepening 

 its channel. The river would deepen its channel, and a time would 



1 As I stated (Geological Magazine, May, 1867, p. 2), the cause of eyery alluvium 

 in the wide wide world is the stoppage of the lowering of the bed of the valley. The 

 sea stops the lowering of the bed of every valley. Therefore the end of every valley 

 next the sea is flat and alluvial. 



