THE OCEAN. 685 



appears to be due to the same pushing and transporting action which 

 forms the ripple-mark ; the commencing push makes the gradual up- 

 slope, — it may be several inches in vertical height, — and then the 

 continued push carries on sands which fall down the steeper front 

 slope, and keep falling, in successive impulses, and so produce a 

 long series of parallel laminae which dip at an angle ordinarily of 20° 

 to 30°. Such deposits may have also the flow-and-plunge structure 

 (p. 82), when the depth is small and the flow is accompanied with 

 plunging waves. With a slower current, ordinary ripple-marks may 

 be made. Wave-action has slight effect on the bottom, and even at a 

 depth of 50 fathoms (p. 659), does not make ripple-marks. 



The stratification in these different deposits is produced on the same 

 general principle with that of alluvial beds, — alternation in the condi- 

 tions of deposition (page 660). It seems surprising that the beds of 

 sand made by the dashing waves over a beach should have structure 

 of any kind ; and yet in most cases the successive layers of deposition 

 are very distinct after solidification has taken place, if not before. It 

 is still more wonderful that the depositions by the plunging wave and 

 the flow of a torrent together should consist of thin layers and show 

 them perfectly in unconsolidated sand and gravel deposits. But in all 

 wave-made depositions and in those formed under subordinate vibra- 

 tions of the water, there is a difference of character in the upper and 

 under parts of each deposited layer, however thin, because of the na- 

 ture of wave or vibratory movements, as already explained. 



The term stratification is used above for : — 



(1.) A bedded structure due to alternations in the time or nature of the supply of 

 material ; in which the layers may be thick, as in ordinary sandstones and limestones, 

 or thin as in most alluvial deposits. 



(2.) A thin-bedded structure which comes from wave-action or vibratory or pushing 

 movements attending depositions, as in the oblique lamination of the ebb-and-flow struc- 

 ture, and the flow-and-plunge structure, and also much of the thin bedding of clayey or 

 earthy deposits, where horizontal instead of oblique. 



(3.) A thin-bedded structure from either of the above sources that (1) gives a fissile 

 character to the deposit, like that of shale ; or (2) that leaves it still solid, as in some 

 compact limestones, which structure is at times undistinguishable by the naked eye un- 

 less over weathered surfaces.. 



Moreover, the term is applied to a formation made of layers, — n* ordinary and right 

 \\<q\ or to a single layer of a stratified rock when it is made up of fine subordinate lay- 

 ers. The limestone just referred to and the cases under No. 2, are stratified in the two 

 senses, that is, (1) in consisting of beds, and (2) in having each bed made up of subor- 

 dinate layers. For the latter of these two kinds the distinctive term straticulate is ap- 

 propriate. Agate, and much stalagmite, are straticulate, but not properly stratified. 



The deposits in the bed of the deep ocean must be without even a 

 straticulate structure, because the waters are unstirred by appreciable 

 currents or vibrations. 



As heretofore stated, the material of the bottom of the ocean, outside of a depth of one 

 hundred feet, consists largely of Rhizopod shells (Foraminifers). Off southern New 



