SCIENCE-GOSSIP. 



1-3 • 



standing as though in relief; whilst the mica was 

 easily removable by scratching. 



It may be safely said that the entire mass of the 

 purest chalU has formed, at some time or other, part 

 and parcel of myriads of living organisms. Fossils 

 are of frequent occurrence in the Chalk, sometimes 

 whole, but as often scattered throughout softer matrix 

 in a fragmentary condition. Such it is, of course, 

 possible to perceive with the unaided e}-e, and classify 

 accordingly, but taken in the bulk, it is found that fifty 

 per cent, is composed of the apparently unfossiliferous 

 matrix itself, which is more acceptably known as chalk. 

 To the unaided vision it appears to consist of nothing 

 more than mineral particles in a fine state of sub- 

 division. It is only under the microscope that the 

 true meaning of these particles is revealed, the 

 apparently shapeless specks resolving themselves into 

 beautiful forms of once living nature. They are, in 

 fact, the shells, or tests, of myriads of minute, almost 



which it would take from i,6oo to 7,000 individuals, 

 placed side by side, to make an inch. These, with 

 their congeners, discoliths, rhabdoliths, and niorpho- 

 lites, have been proved to be of organic origin. Some 

 have apparently formed part of minute protozoans, whilst 

 others are proper to the sea-weeds. Throughout the 

 whole of the chalk, numerous fragments and prisms 

 of shells, corals, polyzoans, sponges, etc., are found ; 

 these, although fragmentary, are recognisable. They 

 have contributed by their weathering in cretaceous 

 times, to the formation of the amorphous powder, in 

 which the various remains are now found. The tests 

 of the foraminifera are of a calcareous nature, and the 

 chalk is therefore a true limestone. On the other 

 hand, when we come to examine the flints, we shall 

 find specimens, equally microscopic, of Radiolaria, 

 another order of the Rhizopoda. 



In order that these minute representatives of life 

 should be able to form such great thicknesses of 



Chalk Pit at Riddlesdown, Sl^rrev. 

 Siiowin^ deposited Strata. 



unorganised organisms, about one-hundredth of an 

 inch in diameter, belonging to the animal sub-kingdom 

 Protozoa (first life). This sub-kingdom contains three 

 sub-classes. One of these, Rhizopoda, branches off 

 into four orders, one of which is the Foraminifera, and 

 to this the minute chalk organisms belong. The 

 classification is as follows : — 



Protozoa 



Gregarinid.\e Infusoria 



Rhizopoda 



I 



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MoNERA Amoeba Foraminifera Radiolaria 



The remaining half of chalk is composed of a great 

 variety of sea-living organisms. Its basis is a fine 

 amorphous powder, whose particles have been derived 

 from the disintegration and decomposition of the 

 shells of molluscs and actinozoans (corals). Con- 

 tained in this are also found numbers of minute oval, 

 saucer-shaped bodies, known as "coccoliths," of 



chalk, as at East Horsley, in Surrey, where in a 

 boring it was found to measure Siyft., the creatures 

 must have existed in inconceivable numbers. Accu- 

 mulated in parts at the bottom of a deep sea of 2,000 

 fathoms there must for ages have been a continual 

 rain of dead shells, leisurely sinking through this 

 depth of water. Arriving at the bed of the ocean 

 they assisted to entomb the remains of other marine 

 creatures, and to form a gradually but very slowly 

 increasing thickness of foraniiniferal ooze. 



Foraminifera have existed from the earliest geologi- 

 cal times, and have left their remains buried in strata 

 of much greater antiquity than the chalk. Large 

 plaster-casts of the numerous species which have been 

 discovered, have been modelled, and these are ex- 

 hibited to the enquirer at the Museum of Practical 

 Geology, in Jermyn Street, London, where the 

 diversity of their forms may be accurately studied. 

 Popularly speaking, a foraminifer may be defined as a 

 speck of jelly, covered more or less by a minute shell 



