t 528 J 



LI. Proceedings of Learned Societies. 



GEOLOGICAL SOCIETY. 



[Continued from p. 460.] 



June 6th, 1917.— Dr. Alfred Harker, F.R.S., President, 

 in the Chair. 



fTHHE following communications were read : — 



1. ' On the Geology of the Old Radnor District, with special 

 reference to an Algal Development in the Woolhope Limestone.' 

 By Edmund Johnston Garwood, Sc.D., F.R.S., F.G.S., and 

 Edith G-oodyear, B.Sc. 



The district comprises an inlier of Archaean grits and Woolhope 

 Limestone forming an elongated dome bounded by Wenlock Shale. 

 It was regarded by Murchison and the Geological Survey as con- 

 sisting of Mayhill Sandstone succeeded conformably by Woolhope 

 Limestone, and they attributed the unfossiliferous character of the 

 sandstone and the abnormal facies of the limestone to alteration 

 by igneous intrusions. Dr. Callaway, in 1900, first suggested that 

 the so-called ' Mayhill Sandstone ' was of Archaean age, and re- 

 corded an unconformity at the base of the limestone. The authors 

 confirm Callaway's views, and give evidence for correlating these 

 Archaean rocks with Prof. Lapworth ; s ' Ba}>"ston Group ' of the 

 Longmyndian. The unconformable relation of the limestone to 

 the Archaean is established in several portions of the district ; while 

 a study of the trilobite and brachiopod fauna of the limestone and 

 included shale confirms the Wenlock age of the deposit. The most 

 interesting fact brought out by a study of the limestone is the 

 important part played in its formation by the calcareous alga 

 Solenopora (of which a new species is described), the deposit 

 constituting by far the most striking development of algal lime- 

 stone yet recorded from British rocks. The limestone represents a 

 reef -facies of the normal Woolhope Limestone, being largely com- 

 posed of bryozoa and calcareous algae. Corals, although present, 

 play only a subordinate part. The reef appears to have grown 

 round a subsiding peninsula of Archaean rocks, which evidently then 

 formed the south-western continuation of the Longmynd range. 

 The same reef -facies is also found to occur at Nash Scar, 3 miles 

 away to the north-east, where it rests on the Upper Llandovery 

 Sandstone. The sudden change to the normal type of Woolhope 

 Limestone at Corton, near Presteign, appears to mark the northern 

 limit of this lagoon phase. 



The paper concludes with an account of the movements that 

 have taken place in the district, to which its general Caledonian 

 trend is due, 



2. 'Correlation of Jurassic Chronology.' By S. S. Buckman 

 F.G.s! 



