these stones are buried a ueasure of the thickness of depoeition 

 since Glacial times? 



_ The failure of sediments to accumxilate, even in deep water in 

 regions where the scouring action of currents or waves is strong 

 le.g.,_the Pourtales Plateau off Florida and the Wyville Thompson 

 p^^^l^'-V ! io^;th Eastern Atlantic) is also geologically suggestive, 

 oan tne fact that Devonian strata have been found lying direct upon 

 Cambrian in certain places, with nothing between, long a geologic 

 puzzle, be credited to similar local scourings in the Paleozoic Sea? 



The presence of glacial pebbles, even boulders, embedded in the 

 bottom on the off-shore banks, in regions such as have been found far 

 out trom the land at various localities on both sides of the iTorth 

 Atlantic, where their presence can not be credited to transport by 

 iioating ice under present conditions, emphasizes the importance of 

 relicts of this sort as evidence of the distances to which the ice 

 sneets of the last glacial period extended out beyond the edges of 

 the modern continents. The information so far gathered on this point 

 IS only enough to whet our appetite for more. And the discovery of 

 ?f;° I'^^"^®^ shells in dredgings from considerable depths marks the 

 importance of submarine evidence of the sort in relation to the 

 possible existence of former land bridges or other areas of sub- 

 sidence. 



So much information has already been gathered from the numerous 

 Dottom samples collected by the various deep-sea expeditions, that 

 further exploration is not likely to seriously alter our general con- 

 ^t^l'-'^'L'^^ the general character of the bottoms of the ocean basins, 

 ^l ntl^'^ peater than, say, 500 fathoms; either as to the structural 

 or chemical composition of the several classes of deep-sea sediments, 

 or as to tneir regional distribution. It is true that our present 

 Charts are largely based on the assumption that within certain ranges 

 01 depth, and at certain distances out from the submarine slopes, the 

 f?«f L+o^l ^^^ superficially clothes the sea floor is so uniform 

 ^^^•L £^°'-'^ points as widely scattered as most of the deep-sea 

 ^°i''il'^^^ ^^""f ^^®^- ^° i^ ^^*ii suffice for the intervening stretches. 

 ?hl ^^s^^elationship that the type of bottom bears to the depth, to 



?« .n^??^''''J ?°'? iJ^*^' ^'""^ ^° "^^^ plankton of the overlying mters, 

 ILll ^^""^""J J^^^ ^^is assumption is generally justified, elcept 



I?^JL-??r i^^^'-i^'^ soundings reveal unexpected shoals or trou^lis 

 dissecting the abyssal plain. ^ 



^.oo TJ^is_ uniformity depends on the rule that the sediments of the 



the shetfp''n/;!ir^^* 'f ^?°'''^- ^^ "oceanic" in origin, consisting of 

 ,^SL^ S-^^ of ^pelagic plants and animals that rain down from above 

 ^^'^^^.^S™ r^^%°''^ ''^^''^ ^^® plankton is abundant, of the skeletons 

 Sitb a^°ni'^.!ii^''^' °;-,°^ ^^^ so-called "red clay" that accumulates 

 ^.i?oo -^ unbelievable slowness from the disintegration of the 

 ?^,^JJ.r°'' J°^°^^^° eruptions, from cosmic dust, and from the pre- 

 ^lllr'^'-?^, of^ manganese and other less common minerals out of the sea 

 fnl^', l^f ^J y®^ *° ?e ^o^e, however, even in the ocean abyss, to 



for tip l^%^f ^""^l^^ ^^^?^ *^^* ^^^^1 ^^^ °^^ °^^^^s, especially 

 Ihlt^Lll^l-^'' and for the Indian, while work recently done shows 

 nSeded ^oaification of mapping of Antarctic deposits is 



