124. 



DR. GU. CALLVWAl' OX THE U-VCOJfJb'ORMITIES UETWEEN 



the Uricoiiiaii area with the even sedimentation of the Longmynd 

 Series. The uniforraity of the strikes and the regularity of the 

 bedding in the latter are too well known to need comment. Even 

 conglomerates, which hardly form beds at all in the volcanic series, 

 can be traced on the strike mile after mile almost from end to end 

 of the Longmynd chain. This change from almost pure vulcanism 

 to pure sedimentation must surelj' indicate a break in time. 



The unconformity between the Uriconian and the Longmyndian 

 is not necessarily a very great one. In so early a period of the 

 earth's history, when the crust was more easily bent and broken, 

 and in a region of energetic vulcanism, new axes of upheaval might 

 be formed with comparative rapidity. Then, too, it must be 

 admitted that the grits and slates of the Longmyndian do not 

 materially* differ in their composition from the grits and mud- 

 stones of the older series. Nevertheless, the unconformity appears 

 to be real, and I submit that the terms " Uriconian " and " Long- 

 myndian " are worthy of a place in our nomenclature. 



DiSCUSSIODf. 



Prof. Blake had not regarded the volcanic rocks as intrusive, but 

 as having burst out from amongst the slates. "Any evidence de- 

 rivable from Lyd's Hole he had shown to be immaterial. The 

 main point in his (the speaker's) paper was the subdivision of the 

 Longmynd rocks into two great groups by an unconformable over- 

 lap betwixt the Upper and Lower groups — the similarit}' of strike 

 being due to subsequent pressure. No satisfactory conclusion could 

 be derived from the examination of a single section such as that 

 at Narnell's Eock; but his assertion of an unconformable overlap 

 had been arrived at after tracing the junction across the district. 

 He had seen fragments in the Lower group like the specimen exhi- 

 bited, and admitted that they were puzzling, as he had mentioned in 

 his paper. It was not of primary importance whether the conglo- 

 merates on Charlton Hill were superficial or not, for he regarded the 

 whole as lying at the very base of the Cambrian. He had no doubt 

 that there was plenty of crushed granite amongst the rocks on 

 Primrose Hill. He was not much concerned in the relations of 

 the Ercal-Hill Red Eock, but would like to know where the rhy elite 

 was entirely surrounded by it. He would ask, if the whole of the 

 Longmynd rocks were to be called Longmyndian, where was the 

 Cambrian of the western part of the district ? 



Prof. Bonnet had seen the Charlton-Hill section, and thought that 

 the evidence was in favour of Dr. Callaway's views, and he might 

 say the same of the Ercal-Hill section. The so-called " chiastolite 

 rock " had been examined by him without finding any sign or pro- 

 bability of the existence of chiastolite. 



Dr. Hicks, so far as his examination of the district had gone, was 

 inclined to follow the Author rather than Prof. Blake. He main- 



* The chief difference is that mica is abundant in the newer series and rare 

 in the older. 



