44. 



KNOWLEDGE. 



[March 1, 1893. 



of dredgings and soundings, made a large number of 

 observations bearing upon the depths of the oceans in 

 different places, the deposits forming, the forms of life 

 flourishing there, and many other interesting questions. 

 But of all such expeditions that of H.M.S. ChaUenyer has 

 been the most fruitful. The Challemjer, with its able staff 

 of naturalists, chemists, and others, under the direction of 

 the late Sir C. Wyville Thomson, left England in 1872. 

 The cruise lasted three and a half years, and since she 

 returned a large number of most valuable and exhaustive 

 reports have been issued. The last of these, published in 

 1892, deals with deep sea deposits, and is the first attempt 

 ever made to deal xcitJi such depositft systt'tnaticallij. It treats 

 of the geology of the sea bed throughout the whole extent 

 of ocean. The authors are Mr. John Murray, naturalist of 

 the Clialltnijev expedition, and the Rev. A. F. Renard, 

 Professor of Geology in the University of Ghent. Our 

 remarks will be chiefly based upon this most excellent 

 report. But, before forming their conclusions, the authors 

 have studied samples obtained by other expeditions, so that 

 the results arrived at are all the more firmly established. 

 Since the return of H.M.S. ChaJlenycr very many samples 

 of marine deposits have been collected from nearly all 

 regions of the ocean basins by various ships. The great 

 majority of these have been examined by them, so that 

 altogether they obtained a very large amount of material. 

 Of pelagic or true ocean deposits, as distinguished from 

 the coarser terrigenous materials laid down nearer to the 

 shores, more than 2000 samples{from depths exceedinglOOO 

 fathoms) have passed through their hands. Indeed, so great 

 is the experience of ocean deposits they have thus gained, 

 that they can even guess with a good deal of certainty the 



region from which a sample submitted to them came, as 

 well as state approximately the depth and distance from 

 land at which it was procured. To test this, they fre- 

 quently asked their assistants to select a sample for them 

 (without giving any clue as to where it came from), and 

 they found that, in nine cases out of ten, they could state 

 the position within a few hundred miles, and the depth to 

 within a few hundred fathoms ! 



In all parts of the ocean where the slope of the sea bed 

 is not precipitous, and where no strong currents sweep 

 over it, the rocky bed (supposed to be the original cooled 

 crust of the earth — in some of the deepest parts) is 

 covered with a mantle of deposits of various thickness, to 

 which the gently-rounded contour of the ocean beds is 

 largely due. Readers of Knowledge will scarcely need to 

 be reminded that, broadly speaking, these deposits consist 

 of (1) sands, gravels and muds (mostly formed near shore) ; 

 (2) finer muds (further out to sea) passing gradually, as 

 (he depth becomes greater, into (3) various organic oozes, 

 such as the well-known "globigerina ooze," which takes 

 its name from a very abundant little foraminiferal shell 

 known as globigerina (on account of its globular shape) ; 

 and lastly (4) the equally well-known " red clay," found 

 in all the deepest depressions of the oceans. And now 

 arises the question of classification, which is not a very 

 easy one. Messrs. Murray and Renard, however, point 

 out that these ocean deposits may be classified either as 

 regards geographical position, or as regards composition, 

 as well as position and depth. In the first case we have 

 the following scheme: — (1) Deep sea deposits ; (2) Shallow 

 water deposits between the 100-fathom line and low water 

 mark ; (.S) Littoral deposits, formed between high and low 



Chaet I. Ocean Deposits. — Explanation. — The white space bordering lands marks the region of Terrigenous Deposits ; vertical 

 lines mark Globigerina Ooze ; horizontal lines mark Red Clav ; broken horizontal lines mark Diatom Ooze ; two areas marked 

 thus ^vX mark Radiolariaii Ooze; dotted spaces mark Coral Sands and Muds; a few small white spaces mark Pteropod Ooze. 



