TRANSACTIONS OF SECTION C. 643 



assumed representatives in the East of Ireland, Wales, and Shropshire. In the 

 former case, which included the beds belonging to the ' Caledonian type,' the for- 

 mation consists of red or purple sandstones and conglomerates ; in the latter, -which 

 included the beds belonging to the 'Hiborno-Cambrian type,' the formation con- 

 sists of hard green and purple grits and slates, contrasting strongly with the 

 former in structure and appearance. 



These differences, the author considered, were due to deposition in distinct 

 basins, lying on either side of an archosan ridge of crystalline rocks, which ranged 

 probably from^ Scandinavia through the central Highlands of Scotland, and in- 

 cluded the North and West of Ireland, with the counties of Donegal, Derry, 

 Mayo, Sligo, and Galway, in all of which the Cambrian beds were absent, so that 

 the Lower Silurian repose directly and unconformably on the crystalline rocks of 

 Laurentian age, as shown in a previous paper. 



As additional evidence of the existence of this old ridge, the author showed 

 that when the Lower Silurian beds were in course of formation, the archsean floor 

 along the West of Scotland must have sloped upwards towards the east, but he 

 agreed with Professor E,amsay, that the crj^stalline rocks of the Outer Hebrides 

 formed the western limit of the Cambrian area of deposition, and that the basin 

 was in the form of an inland lake. 



On the other hand, looking at the fossil evidence both of the Irish and Welsh 

 Cambrian beds, he was of opinion that the beds of this basin were in the main, if 

 not altogether, of marine origin, and that the basin itself had a greatly wider 

 range eastward and southward, the old archtean ridge of the British Isles forming 

 but a small portion of the original margin. 



The Cambrian beds above referred to consist of the Llanberis, Harlech, and 

 Longmynd series, with their representatives at St. David's, in which Dr. Hicks 

 has discovered a primaeval marine fauna. 



1.3. On the Lower Camhrian of Anglesea. 

 By Professor T. McK. Hughes, M.A., F.G.S. 



In this paper the author gives the results of further examination of the base- 

 ment beds of the Cambrian, which he has now traced all along the N.W. flank of 

 the Archasan axis of Llanfaelog. 



He found it resting in some places on gneissic rocks, varying from massive 

 granitoid to fine foliated schistose gneiss, and in other places the Cambrian was 

 seen lying on greenish or blue schist, probably, he thought, the equivalent of part 

 of the Bangor beds. 



But whatever it had below it there was such a similarity in the character of 

 the basement-beds that he had no difficulty in following it and mapping it. The 

 sequence which he found almost invariable was in ascending order. 

 (A) Quartz conglomerate passing up into 

 (,B) Grit, which in turn became finer and passed into 



(C) Sandstones, weathering brown, which got split up in their upper part 

 by thin slabbj- shales (C2). These were succeeded by 



(D) Black shales with subordinate beds of black breccia (D2), and occasion- 

 ally sandstones in the lower part. 



The conglomerate at the base was sometimes very thin, being only a foot or so 

 in one section mentioned. In this case the base of the Cambrian was a kind of 

 gneiss-arkose, which was seen resting on true gneiss, and in the grit and conglome- 

 rate, within twenty feet of the base, he had found abundant specimens of Orthis 

 Carausii. In another section, a few miles off, in the grits within about fifty feet of 

 the base, he had found annelids and fucoids — while in a third case, close by, the 

 basement conglomerate was split into two parts by a bed of black shale some 

 twenty feet thick. 



The brown sandstones and the black breccias had also yielded 0. Carausii and 

 a few other fossils. 



The petrological characters of the basement-beds were generally very constant, 

 though small variations accompanied the dift'erences in tlic underlying rocks. For 



T T 2 



