IN THEIR ROLE AS WORLD-BUILDERS. 7 



fossil condition. The occurrence of this rich series of genera, 

 some of which appear to be confined to this formation while 

 others are hardly known except in the recent condition, suggests 

 that the arenaceous foraminifera have, with few exceptions, always 

 been confined to the deep sea, and that their scanty geological 

 history may be due to that fact, and to the rarity of ancient deep- 

 sea deposits. 



Passing to the Cretaceous period, we find the Neocomian and 

 Aptian strata comparatively devoid of recognisable foraminiferal 

 remains. But it is almost certain that Foraminifera of the 

 smaller types existed in enormous numbers in the seas of these 

 periods, leaving their evidence behind them in the shape of the 

 glauconitic casts and grains which bulk so largely in the Green- 

 sands. 



The Gault of England and the Continent contains a rich and 

 varied foraminiferal fauna running into several hundred species. 

 But although the Rhizopoda must have swarmed in the Gault 

 seas, they do not constitute any large percentage of the total 

 mass of the formation, and are often confined to limited zones. 



The same remark may be applied to the numerous beds of 

 chalk ranging from the Chalk Marl to the Upper Chalk. It is 

 one of those popular beliefs which die so hard that chalk is made 

 up entirely of the shells of the Foraminifera, and the textbooks 

 and microscopical works abound with statements to that effect. 

 Some of the methods suggested to students for the obtaining of 

 specimens can only have originated in the fertile brains of the 

 authors. The beginner is instructed to obtain a lump of chalk 

 and scrub it to fragments with a toothbrush under water ; or to 

 place some lumps in a bag and smash them up with a hammer, 

 subsequently kneading the mass under a tap until the water runs 

 away clear. It is needless to say that such methods can never 

 produce anything but debris and disappointment. These methods, 

 together with directions for the adequate preparation of chalk 

 material for examination, have been fully discussed by Heron- 

 Allen in his " Prolegomena " (23). 



There are very few zones in the Chalk which do not contain 

 Foraminifera, but their number is as a rule small compared with 

 the whole bulk of amorphous matter. But it is probable that 

 in the Chalk sea the Foraminifera really abounded, and 

 that the amorphous carbonate of lime is derived largely from 



