Vol. 60. ] IGNEOUS ROCKS OF THE BRISTOL DISTRICT. 157 



erroneous interpretation which had prevailed and was expressed on 

 the maps of the Geological Survey. The specimens first collected by 

 Mr. Strahan left no doubt in the speaker's mind that the rocks in 

 question formed a volcanic series contemporaneously intercalated 

 in the Carboniferous Limestone. In order to put this question 

 beyond possibility of dispute, he subsequently went over the ground 

 with Mr. Strahan, and the description of the lavas and tuffs given 

 in the ' Summary of Progress of the Geological Survey ' was the 

 result of that visit. His colleague and he could not attempt to 

 define the particular horizon in the Carboniferous Limestone on 

 which this volcanic intercalation lav. nor whether there were more 

 horizons than one. He was glad that their conclusions had been so 

 amply confirmed by the Authors of this paper ; and especially that 

 the definite platform appeared to have been ascertained, on which 

 the records of the Carboniferous-Limestone volcanic eruptions of 

 the Bristol district had been preserved. 



Prof. Watts enquired as to the exact method of occurrence of 

 the variolitic type in the lavas. Was it confined to lavas, or did 

 it occur in rocks the exact origin of which was unknown ? He con- 

 gratulated the Authors on having determined, in this instance, that 

 the volcanic rocks occupied a definite horizon in the Carboniferous 

 Series. 



Prof. Reynolds, in reply to the last speaker, stated that varioles 

 were met with only in the rock from Spring Cove, of the con- 

 temuoraneitv of which there could be no doubt. The varioles onlv 

 occurred in certain parts of the rock. 



