MOKIAN SYSTEM OF RUCKS. 547 



interpretation of the country. The rocks of Howth were deter- 

 mined as Cambrian, mainly because they lie unconformably below 

 Lower Silurians (or Ordovicians). 



Prof. BoNNEY would like to have had stronger evidence as to the 

 interbedding of schists and slates ; he thought that the phenomena 

 might be explained by intense local pressure, whereby a " slatihed 

 schist," so to say, was produced. This was the case elsewhere in 

 Anglesey and in the Alps. Professor Blake had made confusion out 

 of his explanation of the serpentine-calcite rock in Holyhead Island. 

 What he did say in his published paper was that after great crushing, 

 the downward percolation from the once overlying Carboniferous 

 Limestone had helped to cement the serpentine breccias in the 

 Eoscolyn district. A similar thing might be observed in the 

 Apennmes, with this difference, that there the limestone had not 

 been removed by denudation. The halleflinta of the Porth-JSTobla 

 district was crushed-up rock of gneissic origin. He thought there 

 was no necessity for the establishment of the Monian system, and 

 endorsed all the President had said on this subject. The Anglesey 

 crystalline rocks were so much modified by subsequent earth-move- 

 ments that they were generally not very well suited for types. 



The AuTHOE, in reply, thanked the Society for the reception accor- 

 ded to his paper. He admitted the force of the President's remarks, 

 but said that all systems must be based on the careful examination 

 of a single area. He had aimed at simplifying matters by absorbing 

 a number of smaller systems. He instanced the rocks of the Long- 

 mynd and some in Belgium as members of the Upper Monian, and 

 the Wrekin area and St. David's as containing Middle Monian rocks, 

 and suggested that the rocks of the Lizard might be Lower Monian. 

 He thought that Dr. Hicks's criticisms did not leave much to reply 

 to ; on many points they were agreed, except as to the intrusive 

 nature of the granite. He considered that the specimen exhibited, 

 which contained no diorite, satisfied Dr. Hicks's demand. 



He was glad to hear from Prof. Hull the explanation of the Howth 

 beds having been called Cambrian, because it would be equally 

 applicable to prove them Monian. To Prof. Bonney he replied, with 

 reference to the change from slates to schists, that no amount of 

 folding could have done this, since the beds where it occurs are not 

 folded at all. There was plenty of crushed schist in the neighbour- 

 hood, but not of that character. Some hallefiintas might be of 

 gneissic origin, but not all ; very fine fragmentary matter may be 

 produced by the action of volcanos as well as by crushing. He 

 stated that his conclusions had been modified time after time by 

 further knowledge of these Anglesey rocks, and he was now con- 

 vinced that they really constitute one great system. 



