548 Transactions of the Society. 



In the years 1907-8 I made a series of gatherings of* the littoral 

 and shallow- water Foraininifera of Selsey Bill (S.W. Sussex), the 

 description and diagnoses of which were published in a series of eight 

 papers between 1908 and 1911.* Among these gatherings my colla- 

 borator Arthur Earland and T were immediately impressed by the 

 occurrence of some species of arenaceous Foraminifera, a certain 

 restricted number of individuals of which appeared to select and 

 to incorporate among the smaller and normal grains of quartz-sand, 

 of which their shells were constructed, relatively large fragments 

 of coloured gems and other minerals, such as garnet, topaz, and 

 magnetite, which gave a very striking and ornamental appearance 

 to the tests. The incorporation of these fragments afforded food 

 for some reflection, for the specific gravity of these fragments is very 

 much higher than that of the normal quartz-grains — e.g. garnet 

 having a specific gravity of 3* 7-4*1, as against the 2 '65 of quartz. 

 The result of this is that the gem fragments are not normally to be 

 found in the same layers as the quartz, but sooner or later 

 invariably sink below it, a fact which may be demonstrated by 

 dropping a handful of sand mixed with gem dust into a narrow 

 observation-tank, when it will be found that after a little rocking, 

 such as would result from wave action, the gem minerals are 

 accumulated in a thin stratum at the bottom. The method there- 

 fore by which the organisms obtain these heavier grains — and 

 only a restricted proportion of the specimens do so obtain them — 

 is highly problematical. f 



This tendency is observable to a marked degree in specimens 



* Bibliography 1. 



t Mr. Allan B. Dick, who has made a specialized study of the heavy minerals 

 to be found in almost all sands, tells me that the minerals are to be collected 

 separately by pressing a balsam- covered slip upon the wet surface of a sand which 

 has been subjected to the gentle action of moving water. He suggests, not with- 

 out some reason, that such action " elutriates " and carries away the lighter 

 quartz-grains, leaving the heavier minerals temporarily upon the surface, and that 

 they are thus left readily available for the constructional purposes of the organism. 

 If this be the real explanation of the phenomenon, it would appear that when an 

 organism (e.g.Verneuilina polystropha) is found to have used these heavier mineral 

 grains, it has constructed its test in a runnel subject to such movement, whilst if 

 it has not used them it has constructed, or enlarged its shell, in a peaceful pool 

 not subject to such movement, or, whilst attached to alga3 or stones above the sand, 

 from the churned-up and lighter quartz-grains. My only difficulty in accepting 

 this explanation lies in the fact that the great majority of the shells do live upon 

 bottom-sands subject to such movement, and only an infinitesimal proportion of 

 them are found to have incorporated such grains. Haplophragmium agglutinans 

 in the living condition is, in my experience, always found upon waving algte, or 

 attached to the sides of rocks and stones, and practically never in shore scrapings 

 or shallow dredgings, but it is found (ut supra) to display the phenomenon to a more 

 marked degree than almost any other Foraminifera. Further, a Foraminifer is 

 itself so much lighter than even the quartz-grains that the action of the moving 

 water might be expected to remove it with them. (For a full account of Mr. 

 Dick's method and observations, see " Nature,'' xxxvi. (1887) p. 91, and W. 

 Whitaker, " The Geology of London, etc." Geol. Survey, 1889, p. 523.) 



