president's address. 95 



B. Near- Shore Deposits, 



Mr. Murray* has divided the Near-Shore Deposits under four 

 heads, 



{a) Blue and Green Muds, which are met with near the shores of 

 most of the great Continents and Islands. 



{h) Gray Muds and Sands, which are found chiefly near Oceanic 

 Islands of Yolcanic origin. 



(c) Red Mud, which occurs on the Eastern Coast of South 



America. 



(d) Coral Mud, which covers the bed of the Ocean near Coral 



Eeefs. 

 To these may be added 

 {e) Glacial Clays. 



(a) The Blue and Green Muds owe their origin in a great mea- 

 sure to the disintegration of the older crystalline rocks of neigh- 

 bouring land. It has been found that not unfrequently the 

 green colour is however dependent on Grlauconitic particles, 

 and that the shells of Foraminif era in these deposits have become 

 filled with Grlauconite, and are in fact in process of being con- 

 verted into a deposit of ''Grreen Sand." When treated with 

 acid the carbonate of lime is dissolved, and beautiful Glauconitic 

 casts of the Foraminifera remain behind. Such deposits were 

 met with in many places during the ^ Challenger'' s^ dredgings. 

 Instances of this kind were found in the North Atlantic, off the 

 coast of Portugal, that of North America between Halifax and 

 New York, and the eastern side of South America. The Blue 

 Muds descend generally to deeper water than the Grreen, and the 

 Grlauconitic particles rarely occur beyond 700 fathoms, whereas 

 the Blue Muds are frequently in 1,500, and even 2,500 fathoms. 



(h) The Gray Muds and Sands derive their character from the 

 debris of volcanic rocks, and the colour is sometimes so dark as 

 to be almost black. Occasionally these volcanic sands are found 

 as much as 200 miles from the volcanic islands, as, for instance, 



* Proc. Royal Soc, XXIV., p. 518. 



