Vol. 67.] ASSOCIATED ROCKS OF NORTH-EAST MONTGOMERYSHIRE. 417 



Geological Survey. In it, Sir Andrew llamsay mentions the dis- 

 turbed state of the Wenlock Shales in this area, and notes the 

 absence of the grit-beds at the base. With regard to the apparent 

 conformity between the Upper and the Lower Silurian strata in 

 Montgomeryshire, he says that 



' it doubtless arises from the circumstance that during the deposition of the 

 Upper Silurian rocks, the lower strata of this particular area had been but 

 slightly disturbed.' [3] p. 207. 



It will be seen later that this unconformity is greater than he 

 anticipated. In the appendix on the fossils, J. W. Salter noted many 

 specimens from the neighbourhood, as did also Robert Etheridge, 

 in the enlarged edition published in 1881. 



No further work appears to have been done in this district, until 

 J. Eickerton Morgan began his investigations somewhere about 

 the year 1884. In 1890, an abstract of his results was published 

 [5]. He recognized the true age of the Red Conglomerate beds, 

 and stated that they transgress upon ' different zones of the under- 

 lying Ordovician rocks.' The overlying shales, sandstones, and 

 mudstones, he considered to be of Lower Wenlock age. 



About the same time, he wrote two papers dealing with the 

 geology of this part of Montgomeryshire, for the ' Montgomeryshire 

 Collections ' [6], Here, he gave a somewhat fuller account of the 

 different beds occurring in the district, and stated that the Bala 

 Limestone with associated phosphatic beds occurs in Gwern-y-brain. 

 A short list of fossils was also given, to prove the age of the Red 

 Conglomerate beds. His conclusions were, in the main, correct, 

 although some of the shales, considered by him to be of Wenlock age, 

 must be regarded as belonging to the Upper Llandovery. 



Morgan stated his intention to map the base of the Silurian in the 

 area, but his labours were unfortunately cut short by his death. 



In connexion with Morgan's work the late Prof. T. Rupert Jones 

 [8], in 1890, dealt with the Ostracoda from the black shales of 

 Gwern-y-brain. He described several new species, and showed the 

 close affinity of these fossils with North American types. 



In the years 1885 and 1890, Prof. Watts [4] & [7] dealt with 

 the petrology and geology of the Breiddens and the Long Mountain. 

 In the latter paper, he detailed a sequence with graptolite zones 

 from the top of the Bala Beds to the Upper Ludlow. He noted the 

 fact that the Llandovery grits and limestones lie unconformably 

 upon the lower beds, and described a dyke of diabase thrust up 

 along the junction at Cefn, near Buttington. 



Further work on the petrology of the neighbourhood was done by 

 Mr. Jevons [11] in 1904. He opined that certain of the 'diabases ' 

 described by Prof. Watts in the Breidden area are keratophyres. 



In a further paper in 1905, Prof. Watts [12], after determining 

 the age of these rocks to be probably post-Llandovery, welcomed the 

 suggestion that they may be keratophyres, since it would bring about 

 a tendency to unify the type of Ordovician and post- Ordovician 

 intrusive rocks of different areas. 



