Reports and Proceedings — Geological Society of London. 335 



an asby shale, including fragments of ash, andesite, shale, and lime- 

 stone. Interbedded with the conglomerate are bands of limestone 

 and shale, which have yielded fossils of Middle Bala facies. The 

 authors give reasons for maintaining that this conglomeratic series 

 is not due to earth-movement, but is a sedimentary accumulation, 

 though the case is otherwise with a conglomerate developed along 

 a thrust-plane which sepai-ates the volcanic series from an overlying 

 limestone. This conglomerate is compared with one recently de- 

 scribed in the Isle of Man, though the alteration which marks the 

 latter is practically absent from the former. 



Igneous rocks like those found to the north-west of the outlier are 

 also seen at the southern end. 



The general succession of the greatly disturbed Portraine Lime- 

 stone Series from above downwards is : (3) thin-bedded limestone, 

 with shaly partings ; (2) beds of compact crystalline limestone, with 

 many fossils ; (1) thin-bedded limestones, with shaly partings : the 

 upper beds being in places crowded, with corals. This limestone is 

 comparable with the Chair of Kildare Limestone, and also with the 

 Stuurocephaliis, Keisley, and Sholesbrook Limestones of Great Britain. 

 Succeeding the Limestone Series, and separated from it by a thrust- 

 conglomerate, is a Grit Series, which has yielded no fossils, but 

 which resembles the Balbriggan Grits containing black shales with 

 Birkhill graptolites. 



Mr. F. R. C. Eeed, M.A., F.G.S., in an Appendix, gives a list of 

 the fossils found by the authors, and offers some remarks upon the 

 age of the deposits. 



3. " Some Igneous Rocks in North Pembrokeshire." By 

 J. Parkinson, Esq., F.G.S. 



The acid rocks described in this communication are situated at the 

 east end of the Prescelly Hills. Organisms have occasionally been 

 found ; and some discovered half a mile west of Crymmych, at the west 

 end of the area, point to an Upper Arenig or Lower Llandeilo age 

 for the deposits. 



I'he masses of acid rock which occur at Foel Trigarn and Carn Alw 

 show all the characteristics of a true lava-flow. The rock often 

 shows beautifully developed flow-sti-ucture. Some of the rocks are 

 very markedly spherulitic and axiolitic. The axiolitic rocks display 

 an interesting structure which the author believes to be best ex- 

 plained by concluding that during the formation of the axiolitic 

 growths a slight movement occurred in the unconsolidated magma. 

 He gives a full account of the variations which mark the spherulitic 

 and axiolitic structures, and also describes nodular bodies produced 

 by flow-brecciation accompanied by very feeble radial growth, and 

 showing irregular but more or less central quartzose areas. 



After describing a brecciated rock, which on the whole is best 

 accounted for by a process of flow-brecciation, due to a second lava 

 breaking up the first while it was still in a plastic condition, the 

 author describes true pyroclastic rocks, and concludes with a de- 

 scription of the conspicuous intrusive diabases, which, in part at all 

 events, seem to be of the nature of a laccolitic intrusion. 



