MvRCH 1, 1898.] 



KNOWLEDGE. 



1-5 



water mark. la the sejond the avrangement would be as 

 follows :— (1) Pelagia deposits— those l'orm23 towards the 

 centres of the great ooeans, ami chiefly made up of the 

 remains of pelagic organism? (foraminifera, radiolaria, 

 pteropod shells, diatom frastules), along with the ultimate 

 products arising from the decomposition of volcanic rocks 

 and minerals, viz., the red clay ; (2) Terrigenous, or 

 land-derived, deposits — those formed close to continents 

 and islands, and largely made up of transported materials — 

 gravels, sand, muds, &c. The relationsof these two groups 

 to ea^h other, and their subdivisions, are shown in the 

 foUosving scheme which the authors have put forward as 

 the first attempt at a systematic classification, and which 

 combines the two raathods above mentioned. 



1. Deep sea de- 

 posits, beyond 100 

 fathoms. 



2. ;>liallow water 

 deposits, between low 

 water mark and 10[) 

 fathoms. 



3. Littoiul deposits 

 between high and low 

 water mark. 



Red Clay. 

 Radiolarian Ooze. 

 r>iatom Ooze. 

 Globigerina Ooze. 

 Pteropod Ooze. 



Blue Mud. 

 Ke<l Mud. 

 Green Mud. 

 Volcanic Mud. 

 Oiral Mud. 



Sands, gravels 

 muds, &c. 



\ Sands, j^ravels, 

 J muds, &c. 



I. Pelagic deposits, 

 formed in deep water 

 removed from land. 



II. Terrigenous de- 

 posits, formed in deep 

 and shiiUow water 

 close to land masses. 



As we are dealing with deep sea deposits, it will not be 

 necessary to dwell upon those formed in shallower waters 

 (2 and 3). Their characters are well known to all students 

 of geology. They are chiefly due to the action of rivers 



transporting debrin worn off the land ; but they pass at 

 their lower limits into deep sea deposits, and all through 

 show the results of mechanical action. Vegetable and 

 animal life abounds. They occupy about 10,000,000 square 

 miles of the earth's surface out of a total of 190,910,700. 



Passing on to No. 1, it should be pointed out at once 

 that, for various reasons, Messrs. Murray and Renard 

 include in the term deep sea deposits all deposits formed 

 at depths beyond 100 fathoms. This may seem at first a 

 little extreme, for the 100-fathom line, as geographers 

 know, runs very near all the coasts. But this line is one 

 that is well known on our charts, and, secondly, this sub- 

 marine contour line appears to mark the depth at which 

 (on the average) most of the fine amorphous land-derived 

 particles begin to settle down, so that beyond this line 

 are found chiefly fine muds, or organic oozes. Also, at 

 about this depth deposits become more uniform, and signs 

 of mechanical action are much less evident. Between this 

 line and the coasts the deposits are much coarser and more 

 variable. 



Referring to the scheme given here, it will be observed 

 that even deep sea deposits are, some of them, terrigenous 

 or land-derived, and not all organic oozes or red clays. 

 But by choosing a lower limit of depth, it would be easy to 

 make a scheme in which all deep sea deposits were either 

 the one or the other. However, by taking the 100-fathom 

 line, the authors have been able to include in their survey 

 many interesting deposits, the study of which throws light 

 on some important geological problems. 



As a rule, all land-derived material falls on to the bed of 

 the ocean within 100 or 200 miles of the shore ; but in some 

 exceptional cases it may float on to 300 miles or more from 

 the coast. A line drawn 250 miles from all our coasts 



Chaei It- OcEvy CoSTOn&s.—Explamt-ion.—The white space bordering lands marks the shallow waters up to 1000 fathoms— the 

 100 fathom line (not shown) runs near this ; vertical lines mark 1000 to 200O fathoms ; horizontal lines 20O0 to 3000 fathoms ; 

 squares 3000 to -iOOO fathoms ; fine cross over 4000 fathoms. 



