JoNE 1, 1892.] 



KNOWLEDGE 



101 



^V AN ILLUSTRATED "^^ 



MAGAZINE OF SCIENCE 



SIMPLY WORDED— EXACTLY DESCRIBED 



LONDON: JUNE 1, 1892. 



CONTENTS. 



Bv E. Ltdekkee. 



A Lump of Chalk and its Lessons. 



B.A.Cantab. 



Ants Companions. — II. Bt E. A. BrTLEK 



Phosphorus Minabilis. By Vaughax Corxish. B.Sc, 

 F.C.S. ... 



The New Star in Auriga. Bv E. W. M.^uxdeb. F.R.A.S. 



Temporary Stars. By A. C. Ranyaed 



The Flower of Mahomet. By the Rev. Alex. S. Wilsox. 

 M.A.. B.Sc 



Letters :— H. C. ErssELL. Wili.ia-M H. Pickeeixg, T. J. J. 



See, S. E. Peal, C. Grotek 



The Depths of the Mediterranean and Black Seas. 



By Richard Beyxox, F.E.G.S. 

 The Face of the Sky for June. By Heebeei Sadleb, 



F.R.A.S '. 



Chess Column. By C. D. LococK, B.A.Oxon 



PAGE 



101 

 104 



107 

 108 

 ilO 



111 



112 



11 r, 

 lis 



119 



A LUMP OF CHALK AND ITS LESSONS. 



By E. Lydekkek, B.A.Cantab. 



PROBABLY all Englishmen — certainly all those 

 dwelling in the eastern and south-eastern counties 

 — are familiar with the pure white rock which 

 we call, from the Latin rrctn. Chalk. It is indeed 

 this very familiarity which breeds the proverbial 

 contempt, and causes us to take but scant or little notice 

 of what is really a very beautiful substance in itself, alto- 

 gether apart from the interest with which it is invested 

 from a geological point of view. If Chalk were very rare 

 instead of being exceedingly abundant, there is little doubt 

 that it would be reckoned as a beautiful substance, worthy 

 to stand as the best example of a pure white mineral 

 alongside of virgin sulphur as the finest sample of a yellow 

 one. If, moreover. Chalk had happened to have under- 

 gone the action of intense heat under equally intense 

 pressure, it would assuredly have produced an even 

 liner and purer statuary marble than that of Carrara, and 

 might thus have been one of the most valuable of rocks. 



A complaint may not unfrequeutly be heard among those 

 more or less deeply interested in geological science who 

 happen to dwell in a Chalk district, that the very sameness 

 of the Chalk formation throughout England prevents them 

 from finding any interest in the geology of their own 

 districts, and thus leads them to regi-et that their lot had 

 not been cast in regions where a varietv of rocks are to be 



met with. Although there is a considerable amount of 



truth in this complaint, yet if rightly studied the Chalk is 

 so peculiar and unique a form.ition as rather to embarrass 

 us with the number of considerations and problems to 

 which it gives rise, than to be deficient in interest. 



Examining a lump of the pure white Chalk of many 

 parts of England, such as that of Dover, we find that it 

 consists, both to the naked eye and under an ordinary lens, 

 of an exceedingly fine-grained homogeneous soft substance, 

 adhering strongly when applied to the tongue, and leaving 

 a white streak when rubbed on other substances. If 

 treated with vinegar, or any other acid, it will efiervesce 

 strongly with the liberation of the gas commonly known 

 as choke-damp, or carbonic acid, while the base unites with 

 the new acid to form a fresh compound of lime. The 

 lime may be obtained in a pure condition by burning the 

 Chalk, as in a lime-kiln, when the carbonic acid is likewise 

 given ofi' ; and we thus learn that Chalk consists of 

 carbonate of lime. As a rule, when we examine a Chalk- 

 cliff we shall find that the Chalk, although stained here 

 and there with ii'on, is identical in structure throughout 

 great thicknesses, and that it shows nowhere any signs of 

 crystallization. Occasionally, however, as at Corfe Castle, 

 near Swanage, in Dorsetshire, we shall find that the Chalk 

 has become so hard as to leave no distinct streak when 

 rubbed lightly on other substances ; while its cracks and 

 fissures are filled with translucent crystals of white spar — 

 the calc-spar, or calcite of mineralogists. Here then we 

 have the Chalk so hardened, probably by the effects of 

 subterranean heat, as to form what is popularly called a 

 limestone ; while a farther step would have converted it 

 into actual marble. The geologists would indeed apply 

 the name limestone to Chalk, ordinary limestone, and 

 marble indifi'erently ; but since the popular usage is 

 dift'erent, it is well to be assured that all three are but 

 various modifications of one and the same substance. In 

 the north of Ireland the basalt of the Giant's Causeway 

 has converted the Chalk still more completely into a hard 

 limestone. 



Chalk, then, may be defined as a fine-grained, white, 

 non-crystalline, soft limestone. This, however, by no 

 means exhausts the subject of its composition. Thus 

 ;f we take a piece of Chalk and wash it carefully 

 in water with a hard brush so as to reduce it to a 

 state of mud, and examine the portion which falls 

 to the bottom of the vessel under a microscope, we shall 

 find that this is very largely made up of various shell-like 

 substances. Many of these are minute fragments of what 

 may have been real shells, while others are portions of the 

 spines of sea-urchins, and others, again, are the flinty 

 spicules of sponges. By far the larger proportion consists, 

 however, of perfect objects of extremely minute size, 

 mainly belonging to that lovely group of animals known 

 as foraminifers, or shortly, " forams." Of these beautiful 

 little shells some are coiled in a manner recalling the shell 

 of the nautilus, while others consist of globular masses 

 arranged either in a coil or in a straight line, the globules 

 gradually increasing in size from the summit to the mouth 

 of the shell. In all cases, however, the walls of these 

 shells are perforated by the inconceivably minute apertures 

 from which the forams take their name, and through 

 which, when alive, the creatures protruded delicate threads 

 of the jelly-like protoplasm of which their soft parts are 

 composed. Truly marvellous in beauty are these forams, 

 although pages of description can give but a faint idea of 

 them, and the student should see them for himself under a 

 microscope. So numerous, moreover, aie these forams, 

 and other equally minute organisms in the white Chalk, 

 that they frequently compose half its substance, while it is 



