SCIENCE-GOSSIP. 



COLLECTION AND PREJ'ARATIOX OF FORAMIMFERA. 



llv AkiHUK Earlami. 



Collecting. 



T-HE three chief sources from which forami- 

 nifera may be obtaine<i are : — 



:. Dredgings from the sea bottom. With these 

 may be incUided muds from ships' anchors, or cable 

 grapnels, and the debris from fishermen's trawls. 



2. Shore gatherings made between tide marks. 



3- Foraminiferous sands, clays and limestones of 

 various geological ages, especially Cretaceous and 

 Tertiary. 



The method of preparation is essentially the 

 same for materials of the first and second classes. 

 In dredged material, however, the foraminifera as 

 a rule constitute but a small percentage of the total 

 bulk of the material, globigerina ooze being the 

 chief e.tception, whilst in shore gatherings the 

 amount of foreign material present, is largely de- 

 pendent upon the care with which the gathering 

 has been made, and the skill of the collector. In 

 dealing with the fossil materials of the third class 

 considerable deviations from the usual treatment 

 are necessary, varying with the nature and source 

 of the material. 



Not many readers will probably have the oppor- 

 tunity of dredging for themselves, but for the 

 benefit of those who can do so, I will describe a 

 modification of the ordinary naturalist's dredge, 

 which will be found necessary for successful 

 work at the foraminifera. The mesh of the ordi- 

 nary dredge being far too coarse to retain any 

 quantity of sand or mud, it must be surrounded 

 for at least one-third of its length w-ith an outer 

 covering of strong canvas. This must be laced 

 at the upper end to the meshes of the dredge, and 

 extend in a pocket to about eighteen inches beyond 

 the net. The end of this canvas pocket must not 

 be sewn up, but merely tied together with stout 

 cord. After dredging, the sand or mud containing 

 the foraminifera will be found in the canvas bag, 

 and can be removed by untying the cord ; the 

 larger organisms being retained in the dredge. 



Considerable quantities of mud and sand are 

 often brought up by the flukes of anchors, and on 

 the grapnels used in searching for broken cables. 

 The rubbish from fishermen's trawls is also fre- 

 quently productive of good material. These 

 Sources are closed to collectors who have not 

 special opportunities or means to investigate 

 them. The collection of shore gatherings, how- 

 ever, lies within the reach of any microscopist 

 who passes a few days at the seaside. .Although 

 some localities are rich in material while others are 

 poor, there are probably few in which foraminifera 

 are altogclher absent from the foreshore. 



When walking along the sanils between tide- 

 marks, nearly everyone must have noticed the 

 white lines which run along the ripple marks on 

 the sand, and no doubt many have wondered to 



what thev were due. A cursory examination with 

 a pocket lens reveals the presence of many minute 

 shells of a lustrous white colour, with others more 

 or less glassy and transparent, fragments of 

 bryozoa, moUusca, cinders, and other debris. Their 

 presence in these regular lines is due to their low 

 specific gravity as compared with that of the sur- 

 rounding sand grains. The rocking action of the 

 water at the extreme edge of the retreating tide, 

 brings all such light bodies to the surface of the 

 sand. They are left behind in the long ripple 

 marks ; and as the water drains away ihey sink to 

 the bottom of the furrow. Sometimes the material 

 is to be found in extensive patches, or tiny heaps, 

 where an eddy of the tide has caused it to collect 

 in greater quantities than usual. This is espe- 

 cially the case when isolated rocks project above 

 sand, or in the neighbourhood of groynes or piers. 



I have described the deposits as white in colour. 

 This is generally the case, owing to the compara- 

 tive abundance of the Miliolidae, a family that 

 usually occurs abundantly in shore gatherings, and 

 which are characterised by an imperforate test of 

 an opaque and lustrous white colour, resembling 

 china. Hence the name Porcellanea, applied to 

 the group to which they belong. 



In the absence of porcellaneous foraminifera to 

 advertise the presence of the material by their con- 

 spicuous colour, the collector must seek other 

 clues to guide him to the spot. The other two 

 divisions into which the order is separated are the 

 Arenaceous and the Hyaline. The first are rare in 

 shore gatherings, while the second, though present 

 in large numbers, are almost invisible to the naked 

 eye, owing to the fact that their shells, when wet, 

 become nearly transparent. On every coast the 

 tide brings to shore large quantities of floating 

 debris of all kinds, which following the same law 

 as the foraminifera, becomes deposited in more or 

 less regular lines upon the sand, and wherever the 

 collector sees such rubbish accumulated, he may 

 expect to find foraminifera. Round our own 

 coasts, and especially in the neighbourhood of the 

 Thames estuary and the entrances to harbours, the 

 debris consists very largely of coal and cinder dust, 

 derived from steamer refuse. This frequenily 

 shows up in well-defined black lines upon the sand. 

 One very plentiful gathering which I remember 

 making near Heme Bay, in Kent, in which por- 

 cellaneous forms wx're .scarce, was to the naked eye 

 quite black and apparently composed entirely of 

 coal dust. 



I'rom what I have already written, it will be 

 seen that a careful examination of the foreshore is 

 a necessary preliminary to any successful attempt 

 at collecting. The deposition of the material is 

 largely dependent upon the action of wind and 

 tide-set in connection with what may be called 

 the local character of the coast-line, the ]iresence 



