186 Reports and Proceedings — Geological Society of London. 



2. "On the Monian and Basal Cambrian Bocks of Shropshire." 

 By Brof. J. F. Blake, M.A., F.G.S. 



In a previous paper the author had suggested that the Longmynd 

 rocks were referable to the Upper Monian. He now finds that they 

 are divisible into two groups, of which the lower only can be thus 

 referred. 



This lower group is divisible into five parts: — 1. Dark Shales; 

 2. Banded Series ; 3. Furple Slates ; 4. Hard Grey wackes; 5. Bale 

 Slates and Grits. These are shown to have a real dip to the west, 

 and not to be thrown into any folds. It is in these only that fossils 

 have been found. The lowest dark shales are not basal rocks, nor 

 derived from the eastern volcanic series. 



The junction of the upper group, which represents the true 

 Cambrian, is unconformable, as shown by detailed stratigraphy. It 

 consists of three members, the middle one being slates which die out 

 northwards. There is neither synclinal nor anticlinal fold, but a 

 regular sequence and dip ; and pale slates follow on the west. The 

 base is brought into connexion with each division of the lower series 

 except No. 2. The conglomerates contain: — 1. Quartz; 2. Rhyo- 

 lites ; 3. Gneissic rocks ; 4. Slates like those of the underlying 

 group. The supposed Archasan masses on the western border are 

 non-existent, being intrusive and transgressive igneous rocks. 



The volcanic group on the east is not bounded by the main fault, 

 the dark shales lying to the east of that fault. Evidence is given 

 that the volcanic rocks have been protruded through these shales, 

 which they have altered. The Eurite of the Wrekin is of later date, 

 and the only possible older rocks are the Bushton Schists and 

 the fragments of schistose rocks on Brimrose Hill. 



At several places patches of red grit and conglomerate are seen 

 on the Volcanic hills : these are referred to the Cambrian, and their 

 connexion also with earlier conglomerates forming part of the 

 Volcanic series is suggested. The Cambrian quartzite is later than 

 all these, but may be synchronous with the upper part of the 

 western Grits. 



The Volcanic rocks are not, therefore, Middle Monian, as formerly 

 supposed, but represent the interval between Monian and Cambrian. 

 If classed with either, the author inclines rather to place them with 

 the Cambrian, in spite of the unconformity of the quartzite. He 

 regards them as probably the equivalents of the Bangor Series, and 

 possibly of the St. David's Volcanic Group. If this classification 

 be adopted, then the Monian system will be entirely separated from 

 the Bebidian, and be established on distinct and independent obser- 

 vations. 



3. " On a Crocodilian Jaw from the Oxford Clay of Beter- 

 borough." By B. Lydekker, Esq., B.A., F.G.S., etc. 



The symphysis of the mandible of a Thecodont Beptile obtained 

 by Mr. Leeds from the Oxford Clay near Beterborough was described 

 by the author, and reasons were given for referring it to the Croco- 

 dilia rather than to the Sauropterygia. An imperfect skull found by 

 Mr. Leeds in the same formation at Beterborough appears to belong 



