Sept. II, 1879] 



NATURE 



471 



On the Bone-Caves of Derbyshire, by Prof. W. Boyd Dawkins, 

 M.A., F.K.S. — The first cavern discovered was that at Wirks- 

 worth in 1820, accidentally come upon in the workings of a 

 lead-mine. Elephants, rhinoceri, &c., were found there. In 

 1875 the Rev. J. M. Mello explored the caves at Creswell Crag«, 

 which have yielded most important results. Amongst the bones 

 found are those of hyaena, bison, reindeer, lion, hippopotamus, 

 and bear, together with implements of flint and chert, and an 

 engraved bone showing a sketch of the horse. The caves yield 

 evidence of improvement in the manufacture of implements in 

 succeeding dates. In 1876 Prof. Dawkins and Mr. Rooke Pen- 

 nington explored the Windy Knoll, near Castleton. From the 

 mode of occurrence of bones here, it seems clear that the bison 

 was a summer or late-spring resident; the reindeer a winter one. 

 A cavern near Matlock Bath was explored in 1879. 



There is no evidence as to the age of these caverns ; nothing 

 to show that they existed before or during the glacial period. 

 The author deprecated any attempt to place before the public a 

 greater definiteness as regards the date of geological events than 

 the facts warrant. 



On Ammonites and Aptychi, by C. Moore, F.G.S. — The 

 author gives evidence which renders it probable that the apty- 

 chus is not an operculum. It often occurs associated with 

 numerous minute eggs ; and the author suggests that, with the 

 siphuncular tube, it probably represents an ovarian sac. 



On the Classification of the British Pre-Cambrian Rocks, by 

 Dr. H. Hicks, F.G.S. — The author divides the pre-Cambrian 

 rocks into four groups under the following names, in ascending 

 order: — I. Lewisian ; 2. Dimelian ; 3. Arvonian ; 4. Pebidian. 



1. The Lewisian. — So named by Sir R. Murchison to indicate 

 the crystalline rocks of the Hebrides and north-west Highlands 

 of Scotland, is retained to indicate the oldest group at present 

 recognised in Britain, and largely developed in the Hebrides. It 

 is found also in parts of the Malvern Chain, the north-west of 

 Ireland, and possibly also in Anglesey. The prevailing rocks in 

 this group are massive gneisses, in which hornblende and felspar 

 are the chief ingredients, and quartz chlorite and mica but 

 sparingly present. They are usually of a dusky red, grey, or 

 dark colour. Sometimes almost a pure hornblende rock is 

 found. The strike in these beds is usttally east and west, or 

 some point between that and north-west and south-east. 



2. The Dimetian. — This group is largely developed in Wales, 

 as at St. Davids, Caernarvon, Rhos Hirwain, and Anglesey. It 

 has been found by Dr. Callaway in Shropshire, and I have 

 recently seen it with him also in the Malvern Chain, especially 

 in the Worcester Beacon. I noticed it also, last year, in large 

 development at Ben Tyn, Loch Maree, and near Gairloch, in 

 Ross-shire, as well as at several other points in the north-west 

 Highlands of Scotland. The prevailing rocks in this group are 

 granitoid and quartzose gneisses with pinkish, flesh-coloured, or 

 white felspar, and with limestone, micaceous, and occasionally 

 clUorilic and hornblendic bands. Brecciated beds also occur, in 

 which bits of the older Lewisian gneiss are sometimes found. 

 The strike is generally north-west and south-east, or from this to 

 north and south. It evidently overlies the Lewisian unconform- 

 ably in the areas where both have hitherto been found associated ; 

 and its highly quartzose character and lighter colour generally, 

 are in marked contrast to most of the members of that group. 



3. The Arvonian. — At the last meeting of the British Associa- 

 tion I mentioned, for the first time, the discovery, or rather the 

 separation, of this group. It is largely developed in Pembroke- 

 shire and Caernarvonshire. It occurs also in Anglesey and 

 Shropshire, and I have recently found it at the base of the 

 Harlech mountains. I liave seen masses of it also from the 

 Orkneys, and it probably occurs both in the Western Islands 

 and in the Grampians of Scotland. It is the great hiilleflinla 

 group of the Swedish geologists, and the petro-silex group 

 {Hunt) found so largely developed in North America. It is 

 chiefly made up of quartzo-felspathic rocks, sometimes por- 

 phyritic, frequently brecciated, and of compact quartzose rocks 

 or hiilleflintas, which on microscopical examination have the 

 appearance of incipient gneiss. The strike is usually about 

 north and south, and it overlies tlie Dimetian unconforniably. 



4. The Pebidian, — This being the newest group in the pre- 

 Cambrian rocks, is the least altered in character, and most nearly 

 approaches in strike to the overlying unaltered or Cambrian 

 rocks. It resembles that group in many of its roclss, and on 

 that account was for a time supposed to be identical with it, 

 only that it had undergone alterations. Now we know that it 

 underlies the latter unconforniably, and that the apparent simi- 



larity in character is to be attributed to the fact that most of the 

 Cambrian rocks were derived from the denudation of this group. 

 That it was also in a high state of alteration before the Cambrian 

 rocks were deposited upon it is evident from the fact that an 

 abundance of pebbles and masses of it occur in the conglomerates 

 at the base of the Cambrian. It consists for the most part of 

 chloritic, felspathic, talcose, and micaceous schistose rocks, alter- 

 nating with massive and slaty greenstone bands, dolomitic lime- 

 stone, turpentine, lava-flows, porcellanites, breccias, and con- 

 glomerates. It is traversed also frequently by dykes of granite, 

 dolerite, &c. It is a group of enormous thickness, and is largely 

 distributed over Great Britain. It occurs in many parts of 

 Wales, in Shrop^hire, and in Chamwood Forest. I found it 

 also last year in the north-west of Scotland, and I have seen 

 specimens of it collected by Mr. Jas. Thomson and others from 

 Islay, and others of the Western Islands. Dr. Hunt recognised 

 it also along the Crinan Canal, and in the vicinity of Lough 

 Foyle in Ireland. It is probably represented in America by the 

 Huronian group. The prevailing strike is north-north-east to 

 south-south-west, or from this to north-east and south-west. The 

 conglomerates at its base are largely made up of masses derived 

 from the Arvonian, and, at most of the points examined, it is 

 undoubtedly unconformable to that group. 



SECTION D— Biology 

 Department of Anatomy and Physiology 



On a Visual Phenomenon and its Explanation, by Wm. Ack- 

 royd, F.I.C. Abstract of the paper (A). — Visual phenomena are 

 of general interest and are often described, but seldom explained. 

 The phenomenon in question may be seen under the following 

 circumstances. Face the breeze and without winking allow a 

 small rain-drop to fall on the surface of the cornea, all the while 

 keeping your gaze fixed on a lamplight some hundred feet away. 

 As the raindrop alights on the cornea, several rings of light 

 appear to surround the luminous source and they gradi4ally con- 

 tract in diameter. Explanation : 



In sunshine, the moving ring-crest of water, produced by 

 dropping a pebble into a still and shallow pool projects a ring of 

 light on the bottom, which gradually increases in size. The 

 moving ring-crest, by its refractive action, produces a hollow 

 cylinder of rays of ever-increasing diameter, and we see a section 

 of it on the bottom of the pool. The rain-drop falling on the 

 cornea spreads out on its surface in several ring-crests, and would 

 similarly produce a series of outward travelling rings of light 

 were it not for the combined action of the refractive media of 

 the eye. Under the influence of these two hollow cones of 

 light are formed within the vitreous humour directly upon im- 

 pact of the raindrop. The first of these has for its base a 

 small circular area of the hind surface of the lens, and its 

 prolongation ; the second cone has the retina for its base. As 

 any individual ring-crest spreads out on the cornea, the first cone 

 increases in size, the common apex advances towards the retina, 

 and consequently the section of the second cone projected on to 

 the retina decreases in size and appears as a contracting ring of 

 light. 



Department of Zoology and Botany 



Prof. Ray Lankester read a paper. On a Case of Disputed 

 Identity— Hal'physeina. — The dilTerent views of Ilaeckel and 

 others on this remarkable form were discussed, and its history 

 traced. Prof. Ray Lankester, from a careful examination of recent 

 specimens forwarded by Mr. Savile Kent, has no hesitation in 

 stating that it is not a sponge but a curious rhizopod-like ama-ba 

 with a test of sponge spicules curiously constructed like that of a 

 caddis worm. 



Prof. Westwood, M.A., read a paper On the Insects which 

 Injure Books. Referring to an address delivered by Dr. Hagcn, 

 on July 2, 1878, before the American Library Association on the 

 same subject, Prof. Westwood pas ed in review the life-history of 

 the diflerent species of insects which have been fuund to destroy 

 books and printed papers, several of wliich « ere not noticed by 

 Dr. H.agen. The c-iterpillars of the moth Aglossa pinguinalis, 

 and also of a species of Depressaria often injure books by spinn- 

 ing their webs liftween the voluircs and gnawing small portions 

 of the paper with which to form their cocoons. A small mite, 

 Cheyletus eruditiis, is also found occasionally in books kept in 

 damp places. A very minute beetle, I/y/othoiemus erudi.us, 

 forms its tiny burrows within the binding of books. 



