22 GUIDE TO THE FOSSIL INVEETEBEATE ANIMALS. 



Gallery X. The marine Foraminifera, with which geologists are 

 a _e^ease (.j^jg^y concerned, are found on sea-weed and similar objects 

 on the sea-floor, from shore pools down to great depths, and 

 from arctic to tropical waters, sometimes fixed and some- 

 times free ; they live chiefly on diatoms and algae. Most 

 of the Globigerinidae float in the warm surface-water of the 

 great oceans down to a depth of 500 fathoms, and stretch 

 out their pseudopodia along delicate spines ; these eat also 

 minute animals. 



The empty shells are found in all kinds of marine 

 deposits. Numbers are drifted ashore, as at Rochelle and 

 at Dog's Bay, Connemara, whence 124 kinds have been 



b 



Fig. 4. — Foraminifera as Rock-formers, a, Globigerina Ooze, from a depth 

 of 2,760 fathoms in the North Atlantic, x 24 diameters. 6, Forami- 

 nifera washed from Chalk rock near Dunstable, x 36 diameters. 

 (From Chapman's " Foraminifera." By permission of Messrs. 

 Longmans.) 



obtained. An ounce of sand from the Adriatic yielded 

 6,000 shells. Deposits dredged from the sea-bottom contain 

 each a special assemblage varying with the nature of the 

 bottom, depth, and temperature. Such are the coral sands 

 of the Pacific, and the greensands formed at about 500 

 Table-ease fathoms. In the latter the empty shells become filled with a 

 16. green siliceous mineral (glauconite) and often disappear, 

 leaving their casts behind. In the deeper parts of the ocean, 

 especially where the surface is warm, is found an ooze 

 mainly consisting of the shells of Globigerinidae and other 

 pelagic forms (Fig. 4 a); its extent is estimated at 49 

 million square miles, and its thickness must be enormous. 

 Examples of some of these deposits dredged by H.M.S. 



