124 



NATURE 



[June 7, 1900 



when they occur. A few examples will suffice. On pp. 2 

 and 36, the terms " coelomique " and " coelome " refer 

 to a blastocoelic space; on p. 60, "gemmules" is 

 given as an alternative expression to "bourgeons," 

 which arise as outgrowths involving all the layers of 

 the body {e.g. Lophocalyx), whereas on p. 177 the 

 endogenous "gemmules" of Spongilla are rightly de- 

 scribed as special formations, quite distinct from ordinary 

 lateral or exogenous buds, although the buds of Tethya 

 (p. 167) seem to be intermediate between the exogenous 

 and endogenous varieties. On p. 91 (footnote), Sollas's 

 term collenchyme is branded, with other related terms, as 

 "bien inutile," but on p. 152 the superficial cortex of 

 Geodia is characterised as " collenchymateuse." 



In a footnote on page 203, we are reminded that 

 H. J. Carter instituted a comparison between the flagel- 

 lated chambers of sponges and the branchial sac of 

 Ascidians. The authors add that this comparison 

 " nous semble bien singuli^re aujourd'hui ou ces etres 

 sont mieux connus." On the contrary, the comparison 

 is appropriate, the analogy between the flagellated 

 chamljers of a sponge (in respect of their respiratory 

 and nutritive functions and of their relations to the 

 inhalent and exhalent canals) and the branchial sacs 

 of the Ascidiozooids in a compound Tunicary (cf. 

 especially the Didemnidae) being an extraordinarily 

 close one ; but of course Carter was innocent of the dis- 

 tinction between homology and homoplasy. What is 

 very singular indeed is the fact that, in these latter 

 days, the same fatal confusion between actual physio- 

 logical conditions and abstract genetic relationships is 

 constantly being repeated. A. W. 



THE DURATION OF THE BRITISH 

 COAL-FIELDS. 



Les Charbons Britanniqiies ei letir epuisement. By E. 

 Loze. Pp. ix -1- 559, and vii + 562 to 1229. (Paris : C. 

 Beranger, 1900.) 



IN France, as in the rest of Europe, consumers have 

 during the past winter been complaining of the 

 difficulty of obtaining an adequate supply of coal, the 

 chief cause of the increased demand having been the 

 activity in the iron and steel trades. At the same time, 

 prolonged strikes in Austria and elsewhere, and the tem- 

 porary cessation of the production of the collieries of 

 Natal and Cape Colony, have lessened the supplies 

 usually available. The prevailing scarcity of coal is a 

 matter of serious moment to France, where, owing to the 

 increasing depth of the collieries and the costly nature 

 of mining operations, the quantity of coal that has to be 

 imported from other countries grows larger every year 

 At the present time about two-thirds of the coal consumed 

 in France is raised in the country ; and last year the im- 

 ports amounted to 10,500,000 tons, of which quantity 

 6,000,000 tons were obtained from Great Britain. France 

 being so largely dependent on Great Britain, it will 

 readily be seen that the duration of the British coal-fields 

 is a subject of no little importance to French economists. 

 M. Loze has, therefore, been induced to devote two 

 bulky volumes, covering together 1229 pages, to a critical 

 consideration of the investigations of Prof. Stanley Jevons, 

 the Right Hon. Leonard H. Courtney, Mr. R. Price- 

 NO. 1597. VOL. 62] 



Williams, Mr. T. Forster Brown, Prof E. Hull and othe 

 English writers. 



The results of his studies are grouped in four sections. 

 The first contains an account of the geography of the 

 British Isles, with historic, geological and economic 

 details. The second section contains a detailed de- 

 scription of each of the British coal-fields, with a chapter 

 on the coal resources of the Colonies. The third section 

 deals with commercial geography, water and railway 

 transport, and the principal industrial centres. The 

 fourth and last section contains an estimate of the coal 

 supplies of the United Kingdom, with a summary of the 

 views expressed as to their probable duration. The 

 work concludes with a lengthy appendix dealing with 

 cognate matters, the production and consumption of 

 mineral fuel in various parts of the world, the consti- 

 tution of the British Colonial empire, the navy and the 

 army. 



In discussing the views of the various authorities, the 

 author prefers to accept the pessimistic forecast of Mr. 

 T. Forster Brown rather than the optimistic estimate of 

 Prof. Hull. Mr. Forster Brown calculates that the 

 amount of coal of good quality remaining in the United 

 Kingdom at a depth not exceeding 2000 feet, the depth 

 that he regards as the limit of economical mining, is 

 15,000 million tons. Such is the supply on which Great 

 Britain must base its hopes in the inevitable economic 

 conflict with the United States. In spite of the care and 

 accuracy with which the divergent views on the subject 

 are set forth, it may be doubted whether the author has 

 made out a clear case for rejecting Prof Hull's estimates, 

 which show that the amount of coal remaining within a 

 depth of 4000 feet is 81,683 million tons. The criticism 

 of Prof Hull's views is not convincing, inasmuch as M. 

 Loze, who does not appear to possess a practical know- 

 ledge of geology and mining, has not followed the recent 

 investigations as to the limits at which mining may be 

 carried on with profit. At the present time the greatest 

 depth at which in Great Britain mining operations may 

 be carried on has been reached at the Pendleton colliery, 

 near Manchester, where the deepest workings are nearly 

 3500 feet below the surface. This enormous depth has, 

 moreover, been exceeded in other countries, notably in 

 the Lake Superior district, where a shaft of the Calumet 

 and Hecla copper mine has now attained the record 

 depth of 4900 feet, and in Belgium, where a colliery at 

 Mons is 3937 feet deep. Depths such as these show that 

 the limit of depth of 4000 feet assumed by Prof Hull is 

 well within the bounds of possibility. In view of the 

 marvellous efficiency of modern winding-engines, no con- 

 siderations of a mechanical nature need limit the pro- 

 spective depth of shafts. By far the most important 

 obstacle to very deep mining is the increase of tem- 

 perature in proportion to the depth. Here, again, the 

 author is apparently not familiar with recent observations. 

 Since 1848 and 1854, the dates of observations cited by 

 him, methods of determining earth temperatures have 

 been greatly improved, and the results recently obtained 

 at the Paruschowitz borehole in Silesia, put down by the 

 Prussian Government to a depth of 6573 feet, show an 

 increase of temperature of 1° F.for every 621 feet. This 

 rate of increase would not present an insuperable obstacle 

 to mining at a depth of 4000 feet. 



