TRANSACTIONS OF SECTION C. 351 



The Palmocorynce were next alluded to, and the author said that he had 

 identified all the species and forms of Palceocorijnce that had been figured by Dr. 

 Duncan in his various papers. But the conclusion the author had arrived at was, 

 that these so-called organisms were neither Hydroid, as was supposed by Dr. Dun- 

 can, nor foraminiferal, as was suggested by Dr. Allman — all the forms were refer- 

 able to species of Fenestella and Polypora. Although this opinion was given with 

 some confidence, the author was not prepared to say at present that the whole of 

 Dr. Duncan's views were illusive. There can be no doubt but that the forms P. 

 scotica were really infertile processes; but P. radiata had presented so many 

 peculiar details to the author, that until he had satisfied himself as to the nature 

 and purpose of this structure in the Polyzoary of the Polyzoa, he was not prepared 

 to substantiate that Dr. Duncan had given an erroneous judgment. Although P. 

 radiata may turn out to be after all a portion of Fenestella, and not a parasite. 1 



5. On the Classification of the British Pre-Cambrian Bocks. 

 By Henry Hicks, M.D., F.O.8. 



The author divides the Pre-Oambrian rocks into four groups, under the follow- 

 ing names, in ascending order : 1, Leioisian ; 2, Dimetian ; 3, Arvonian ; and 4, 

 Pebidian. 



1. The Leioisian, so named by Sir R. Murchison to indicate the crystalline 

 rocks of the Hebrides and North- Western Highlands of Scotland, is retained 

 for 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 red 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 usually E. and W., or some point between that and N.W. 

 and S.E. 



2. The Dimetian. This group is largely developed in Wales, as at St. David's, 

 Caernarvon, Rhos Hirwain, and Anglesey. It has been found by Dr. Callaway 

 in Shropshire, and I have recently seen it in the Malvern chain, especially in 

 the Worcester Beacon. I noticed it also last year in large development at Ben 

 Fyn, Loch Maree, and near Gairloch in Ross-shire; as well as at several other 

 points in the North-Western Highlands of Scotland. The prevailing rocks in this 

 group are granitoid and quartzose gneisses, with pinkish, flesh-coloured, or white 

 felspar; and with limestones, micaceous, and, occasionally, chloritic and hornblendic 

 bauds. Brecciated beds also occur, in which bits of the older Lewisian ouieiss are 

 sometimes found. The strike is generally N.W. and S.E., or from this to N. and 

 S. It evidently overlies the Lewisian unconformably in the areas where both have 

 hitherto been found associated, and its highly quartzose character and lighter 

 colour generally is in marked contrast to most of the members of that group. 



3. The Arvonian. At the last meeting of the British Association I mentioned 

 for the first time the discovery, or rather the separation, of this group. It is largely 

 developed in Pembrokeshire and Caernarvonshire. It occurs also in Anglesey and 

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

 heart of the Harlech mountains. I have seen masses of it also from the Orkneys, 

 and it probably occurs both in the Western Islands and in the Grampians of Scot- 

 land. It is the great Halleflinta 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 porphyritic, frequently brecciated ; 

 and of compact quartzose rocks or halleflintas, which on microscopical' examination 



1 Many particulars respecting Palceocorynat will be published in Science Gossip 

 for this year, and the greater bulk of the latter part of the above paper will be repro- 

 duced and fully discussed.— G. R. V. 



