SUBMARINE DEPOSITS 189 



section through the Atlantic from Tristan d'Acunha to 

 Ascension Island, wherever the depth is less than 1,000 

 fathoms Pteropod ooze is found capping the elevations, 

 while the depressions between are occupied by Globigerina 

 ooze. It occurs in similar manner on several isolated spots 

 in the Pacific and Indian Oceans. 



2. Globigerina Ooze, — A calcareous deposit covering nearly 

 50 millions of square miles on the floor of the ocean in deep 

 water, but not in the greatest depths. It is not found in 

 cold seas, but elsewhere is widely distributed in depths of 

 1,000 to about 2,500 fathoms, and is especially character- 

 istic of the North Atlantic, where it occupies 9 million square 

 miles, nearly 40 per cent, of the area. It was first made 

 known from the soundings of cable -laying steamers in the 

 North Atlantic, described by Ehrenberg and Bailey (1853), 

 and later by Wallich, Wyville Thomson, Carpenter, and 

 others ; and is carried far north into the Norwegian Sea 

 by the effect of the Gulf Stream on the surface organisms. It 

 is also found in the Indian Ocean, the South Pacific, and 

 the Southern Ocean, but is almost absent from the North 

 Pacific. 



This deposit is formed mainly of the shells of Foraminifera 

 which live in the surface waters, and of these the most 

 abundant and characteristic is G^Zo6?^en7io^ hulloides (Fig. 10), 

 although other allied species and genera are also commonly 

 present, along with the calcareous Coccoliths and Rhabdoliths 

 derived from minute surface algae. Many other organisms 

 are represented, but the relatively large and strong Globi- 

 gerina shells mask the others and appropriately give their 

 name to the deposit (see Plate XII, Fig. 1). Some idea of 

 the kind of rock that might be formed from Globigerina ooze 

 may be obtained by consolidating and sectioning a sample 

 of the deposit (see Plate XII, Fig. 2). 



The proportion of lime varies in samples of Globigerina 

 ooze at different depths, from 30 to 90 per cent., the average 

 being about 65. The deposit is in its most characteristic 



