NATURE 



[January 5, 1922 



though within certain limits both take place freely. 

 Lindau, however, has described how in certain 

 hypophloeodlc lichens the alga actually forges 

 ahead of the fungus. 



The various branches of the subject have been 

 very fully dealt with by Miss Lorrain Smith, but 

 we think that not sufficient reference has been 

 made to Exsiccata, which have played such an 

 important part in lichenological nomenclature. 

 We also consider that the book as a whole is not 

 well illustrated. Many of the line drawings are 

 quite inadequate as illustrations in a handbook of 

 this standard. The half-tone figure on p. 117 

 appears to us to be Cladonia uncialis rather than 

 Cladonia furcata, whilst Fig. 135 on p. 416 does 

 not recall to us Parmelia omphcdodes, which it pur- 

 ports to represent. Apart from these blemishes, 

 which we consider rather serious, the handbook 

 is a storehouse of valuable information, and Miss 

 Lorrain Smith deserves the thanks of all lichen- 

 ologists and botanists for the care and thorough- 

 ness with which she has completed her task. 

 Some readers might possibly object that they are 

 left too much to draw general conclusions for 

 themselves. 



The price of the book, unfortunately, is prohibi- 

 tive except for public and college libraries. 



(2) We are sure that Miss Lorrain Smith's 

 " Handbook of the British Lichens " will answer 

 its purpose very well and help both botanist and 

 collector to name their specimens, instead of being 

 compelled to depend for this on foreign books. 

 The book, however, is only a key to the "Mono- 

 graph of the British Lichens/' by Miss Lorrain 

 Smith, the price of which, again, is well-nigh pro- 

 hibitive. We may express the hope that this little 

 book will help to create renewed interest in a 

 group of plants the study of which was at one 

 time keenly followed in this country. 



O. V. D. 



British Mineral Resources. 



Memoirs of the Geological Survey. Special Re- 

 ports on the Mineral Resources of Great Britain. 

 Vol. 19, Lead and Zinc Ores in the Carbon- 

 iferous Rocks of North Wales. By Bernard 

 Smith. Pp. iv+ 162 + 3 plates. 192 1. 55. 6d. 

 net. Vol. 21, Lead, Silver-lead, and Zinc Ores 

 of Cornwall, Devon, and Somerset. By Henry 

 Dewey. Pp. iv + 72. 192 1. 25. 6d. net. 

 (Southampton: Ordnance Survey Office; Lon- 

 don : E. Stanford, Ltd.) 



THE two volumes under notice form an im- 

 portant contribution to our knowledge of 

 British mineral deposits, and afford satisfactory 

 evidence that Dr. Flett is continuing energetically 

 NO. 2723, VOL. 109] 



the valuable series of reports inaugurated by his 

 predecessor at the Geological Survey. The scheme 

 of both volumes is identical and is upon the lines 

 with which previous reports had already familiar- 

 ised us, but the economic importance of the de- 

 posits discussed therein differs very widely. The 

 lead and zinc veins of North Wales have not only 

 been highly productive in the past, but also may 

 well take rank in the future among the leading 

 British lead-producing mines, whilst those of the 

 south-west of England present little more than 

 academic interest. Needless to say, none of the 

 mines discussed in either volume is at work just 

 now ; in fact, in the whole of Great Britain there is 

 not a single lead or zinc mine capable of working 

 save at a loss at the present time, probably a 

 result of Government interference in the control 

 of industries. 



In North Wales such well-known mines as the 

 Halkyn mines and others in the Holywell-Halkyn 

 area, the Minera mines and other adjoining mines 

 in Denbighshire are fully described, together with 

 numerous less important mining properties. It 

 is abundantly clear that in all these cases the 

 great difficulty to be overcome is the enormous 

 influx of water, which has rendered the economic 

 working of these mines practically impossible. An 

 interesting account is given of the various deep 

 adit drainage schemes by which it is proposed to 

 unwater some of the more important mining areas 

 down to a considerably greater depth than has 

 hitherto been reached. Although he does not 

 specifically say so, it would appear that Mr. 

 Bernard Smith entertains no doubt of the ore 

 holding down to the greatest depth that would 

 thus be rendered available. Incidentally he shows 

 that the 35,000!. which the Government advanced 

 for unwatering the Halkyn area have been wasted 

 and have never yielded any return whatever. It 

 can only be hoped that some satisfactory scheme 

 for unwatering this area may be devised and 

 carried into execution, though it is difficult to see 

 how this can be done until British lead-mining 

 reaches a sounder economic position than that 

 with which it is faced to-day. 



As regards the lead mines in Cornwall, Devon, 

 and the Mendip Hills, it can only be said that 

 there is practically no likelihood at all of any 

 serious revival of the lead-mining industry in these 

 parts, and it is fortunate that the task of collect- 

 ing information as to the past history of these 

 mines has been undertaken before it is too late. 

 Mr. Dewey has done a useful piece of work in 

 carefully compiling an account of these mines, 

 which will be especially interesting to the student 

 of mineral deposition. H. Louis. 



