April 1, 1899. 



KNOWLEDGE. 



79 



carbon bag been found to be coke, and unslaked lime is 

 preferred to slaked lime. 



The following account refers to the method of production 

 employed at the Willson Aluminium Company's Works. 

 The coke, containing from seven to ten per cent, of ash, is 

 pulverised and mixed with ground lime, containing about 

 one and-a-half per cent, of magnesia, and not more than one 

 per cent, of other impurities, sixty-four to sixty -five parts of 

 coke to one hundred parts of lime being used. The mix- 

 ture is charged into an iron car, the bottom of which 

 ia covered with a layer of carbon, which forma one 

 of the electrodes, and is connected with the dynamo con- 

 ductor by a clamp, fixed to a projection on the car by 

 a screw. 



The other electrode consists of twelve carbon pencils, 

 each four inches square and thirty-six inches long, 

 dovetailing into a holder, and surrounded by an iron 

 jacket to minimise waste by oxidation. This electrode 

 is connected with the dynamo by a copper bar enclosed 

 by iron slabs, and its height is adjusted by means of 

 a chain operated by a screw, as the current is found to 

 vary from the amount required. 



The charge ia run into the car through shoots, aided 

 by four-bladed feed rods. The car is automatically 

 moved to and fro about two inches, twenty times a minute, 

 by means of a rod, to keep the mass compact. The 

 gases evolved during the reaction escape at a chimney, 

 and a cold-air jacket is also provided. Doors are fitted 

 to the furnace. The charge covers the pencils to a 

 height of about twelve inches. 



The best yield has been found to be produced by a one 

 hundred volt current and one thousand seven hundred to 

 two thousand amperes. The carbide is obtained in the 

 form of an ingot, the inner portion of which is almost 

 pure. Around it is a less pure carbide, containing fifty to 

 seventy per cent, of carbide, while this, again, is surrounded 

 by the unaffected charge which is used again. The pure 

 and second rate carbide are usually broken up together so 

 as to yield a mixture which gives five cubic feet of acetylene 

 per pound of carbide, instead of 5'89, the theoretical 

 amount under ordinary atmospheric conditions. 



At the extensive Swiss works, where the cheap water 

 power has given rise to the erection of several large 

 carbide plants, the method of production is somewhat 

 different, the reduction being performed in crucibles and 

 the product usually drawn off while liquid. The selling 

 price of the Swiss carbide is now about forty centimes per 

 kilogramme (2*2 lb.), say £16 per ton, for quantities of 

 over a ton. According to Korda, the cost of production 

 at present never falls below £10 per ton. 



SECRETS OF THE EARTH'S CRUST. 



By Gkenville A. J. Cole, m.r.i.a., f.g.s., Professor of 

 Geology in the Royal College of Science for IrelMid, 



II.— THE OLDEST FAUNA OP THE GLOBE. 



PRIOR to the publication of Darwin's " Origin of 

 Species," most geologists would have been content 

 to regard the oldest known fossil fauna as truly 

 that which was first formed upon the globe. The 

 Cambrian strata, investigated by Prof. Sedgwick 

 about 1810, were seen to contain a considerable number of 

 organic remains ; but these were obviously more obscure 

 and " primordial " in type than those found, in such 

 wealth of variety, in the overlying SUurian beds of Murchi- 

 son. Even when, in 1846, Barrande had revealed the 

 beauty of preservation of the Cambrian fossils of Bohemia, 



the absence of any evidence of previous organisms made it 

 natural to suppose that life itself sprang into existence at 

 this horizon. The arguments that were fully justified only 

 sixty yeara ago are well expressed in the words of Mr. 

 .Joshua Trimmer : — ^' 



" The rocks of the Cambrian group .... occur at but 

 few points, and in small quantities, amidst a great thick- 

 ness of sedimentary rocks, extending over a wide area, and 

 this circumstance, connected with the paucity of species 

 where the fossils are in the greatest abundance, appears 

 favourable to the presumption that the absence of organic 

 remains from the older stratified rocks of the mica slate 

 and gneiss systems is not the effect of any process by 

 which they have been destroyed, and that in the Cambrian 

 rocks we behold the first appearance of organic life upon 

 the surface of our planet." 



Prof. John Phillips, in devising the terms Palieozoio, 

 Mesozoic, and Cainozoic, recognised that we must divide 

 up geological time by the succession of faunas, as estab- 

 lished by Wilham Smith in 181.5. The base of the Paleo- 

 zoic or " old life " group has long been fixed at the bottom 

 of the Cambrian system. Any strata earlier than that 

 horizon became styled Azoic (devoid of life) or Eozoio 

 (dawn of life), according to the philosophy of the writer. 

 Nowadays, the terms Archaean and Precambrian, which 

 commit us to no opinion, are employed for this most 

 ancient group. It is obvious that one of the profoundest 

 secrets of the earth's crust has been entrusted to the 

 Precambrian strata. 



Mr. Trimmer, as above quoted, and his contemporaries, 

 commented on the absence of organic remains from the 

 " mica slate and gneiss systems," the fundamental rocks 

 on which so many of our Cambrian beds repose. Even 

 if these old rocks result from the metamorphiam of 

 sedimentary masses, it is extremely improbable that fossils 

 could remain in them unharmed. In recent yeara, more- 

 over, it has been made clear that the banded structures of 

 schist and gneiss, so long relied on as indications of a 

 sedimentary origin, are commonly due to flow of the mass, 

 or, in some cases, to the penetration of one rock by another 

 in thin parallel sheets. Scrope and Darwin 1 long ago 

 ascribed these foliated structures to flow in a non- 

 homogeneous body; but the truth of their observations 

 was overlooked for half a century. The result, however, 

 of the acceptance of their views is that few are likely to 

 look for fossUs on the foliation-planes of an Archsan 

 schist. It chances that here and there, among Paleozoic 

 schists, some remains of organisms have survived; bat 

 their broken and distorted condition offers little hope to 

 the student of more fundamental masses. 



In many parts of the globe, however, we find unmeta- 

 morphosed and clearly stratified rocks, underlying the 

 lowest Cambrian, and resting unoonformably on the ancient 

 metamorphic series. Thus the normal types of sediment 

 by no means begin with the fauna studied by Sedgwick 

 and Barrande. It has become, indeed, necessary to set a 

 limit to the Cambrian deposits, a limit which shall at the 

 same time mark the close of the mysterious Archa3an era. 



Such a limit haa been found in what ia called the 

 Olenellus zone, or, better, the Olenellus series. Just as it 

 ia convenient to claaaify the Cretaoeona beda by their 

 prevalent sea-urchins, or the Jurassic beda by their 

 ammonites, or the Ordovician and Silurian by those obscure 



» " Practical Geology and Mineralogy," 1841, p. 199. 



t See, for instance, G. P. Scrope, " Geology of the Ponza Isles," 

 Trans. Geo!. Soc, 1824, p. 228 ; and Darwin, " Geol. Observations 

 on Volcanic Islands," end of chapter iii., and " Geol. Obs. on S, 

 America," end of chapter tI, 



