DYNAMICAL GEOLOGY. 245 



Foraminifera in certain fresh samples of ocean deposit. But 

 it was not until 1871, by means of the Challenger Expedition, 

 that any approximate estimate of the composition of typical 

 pelagic oozes could be formed. The report by Murray and 

 Renard (1891) on deep-sea deposits discloses the great import- 

 ance of Globigerina ooze, which covers the floor, more espe- 

 cially of the central portions, of the Pacific Ocean, and is 

 found at depths as great as 2,600 fathoms. It is more widely 

 distributed than any of the other organic ocean muds, the 

 Pteropod calcareous ooze, the siliceous ooze composed of 

 diatomaceous material, or the Radiolarian siliceous ooze which 

 is limited to very great depths of the ocean-floor. Littoral 

 deposits are more mixed in character, usually comprising 

 Molluscan, Bryozoan, and Echinoderman remains, although 

 occasionally beds of individual types occur. Recent littoral 

 deposits, on account of their more accessible position and the 

 larger size of the faunas, have long been familiar to scientific 

 observers, and were the first to be compared with fossil faunas 

 in the rocks. 



The activity of reef-building coral zoophytes has been one 

 of the most interesting themes in modern scientific research. 

 The red coral of the Mediterranean Sea was highly prized by 

 the nations of antiquity for its beauty, and has always been an 

 article of commercial importance. The first mention of the 

 coral growths in the Red Sea was by the Portuguese writer, 

 Don Juan de Castro; in 1616, Pyrard described the coral 

 atolls of the Maldive Islands; and in 1742, Peter Forskal by 

 a series of investigations on coral reefs determined that the 

 calcareous material for their construction was separated from 

 sea-water by a small sedentary polyp. The closer study of 

 the coral animal has shown it to be an ally of the Sea- 

 Anemone or Actinian polyp, from which it is distinguished by 

 its habit of growing as colonies, and of building up calcareous 

 skeletal supports for the soft fleshy parts. 



Geology has contributed 'a vast store of information about 

 the skeletal structures of reef-building corals in past geological 

 epochs, and at the present day few questions are of such 

 common interest to the various branches of natural science as 

 those concerning corals the determination of the present 

 geographical distribution of coral reefs, the climatic and 

 physical conditions of growth, the chemical transformations 

 undergone by the skeletal structures after withdrawal of the 



