1862.] HULL CARBOKEFEEOUS STEATA. 129 



limestones are being accumulated in a clear ocean*. If we take the 

 North Atlantic, we find reason for believing, on the evidence of the 

 deep-sea soundings, that the central area is composed of a fine cal- 

 careous mudt, the production of Foraminifera and other marine ani- 

 mals, while along the shores of the American continent and those 

 of Europe deposits of sand, gravel, and claj are in course of accumu- 

 lation. If these regions were elevated into land, we should probably ' 

 find a formation composed in one direction of limestone, like chalk, 

 and in the other of sandstones and shales, both classes of material 

 being developed from opposite areas of dispersion. 



Indeed, the representative positions of the pelagic and Kttoral for- 

 mations — the one calcareous, the other sedimentary — are very clearly 

 stated by Sir C. Lyell, who says t, ''It has been ascertained by sound- 

 ings in all parts of the world, that where new deposits are taking place 

 in the sea, coarse sand and small pebbles commonly occur near the 

 shore, while further from land and in deeper water finer sand and 

 broken shells are spread over the bottom ; stiU further out, the 

 finest mud and ooze are alone met with. Mr. Austen observes that 

 this is the rule in every part of the English Channel." I think, how- 

 ever, that experience will bear us still further than this, and that 

 we may regard the predominance of sedimentary strata as highly 

 unfavourable to the development of calcareous, in the same group of 

 rocks. 



(5.) The same general principle is in force over our globe at the 

 present day, and probably has been from the times when calcareous 

 strata, which are the representatives of marine life, first began to be 

 formed. Wherever large rivers pour sediment into the ocean, or 

 where currents take up and distribute this sediment over the sea-bed, 

 there limestones will be very sparingly formed. On the other hand, 

 where, from certain causes, such as the great distance from land, or the 

 absence of such rivers and currents, the water of the sea is clear and 

 free from mud within the temperate or tropical regions, there calca- 

 reous matter will be accumulated. Of the strata at present forming, 

 the great calcareous members are to be found occupying principally 

 mid-oceanic regions, and their representative sedimentary members 

 range themselves in the direction of the coasts. StiU there may be 

 frequent cases where the limestones may be formed along the coasts 

 of large tracts of land, as on the shores of Australia and Southern 

 India, but in every such case there is an absence or scarcity of sandy 

 or muddy sediment §. Keverting to geologic periods, I have no wish 

 here to repeat what has been frequently shown by Lyell, Darwin, 

 Phillips, Godwin-Austen, and other writers, that calcareous forma- 



* For this illustration I am indebted to my friend Dr. J. Hector, lately Surgeon 

 and Geologist to the exploring expedition under Capt. Palliser. 



t Capt. Maury's ' Physical Geography of the Sea.' A very interesting account 

 of these soundings has been published by Dr. Wallieh for private distribution. 



X 'Principles of Geology,' 8th edit. p. 770. 



§ On this point Ehrenberg states " that he never saw corals grow where the 

 sea was frequently rendered turbid by shifting sand, but ony where it was clear 

 and pure."— PoggendorJBf's Annalen. The same fact is stated by Mr. Jukes, 

 Mr. Darwin, and other writers. 



VOL. XVIII. PAET I. K 



