Vol. 60.] IGNEOUS ROCKS OF THE BRISTOL DISIRICT. 155 



rods of peroxidized magnetite. The red calcareous ash, of the more 

 easterly section, is the most conspicuous of all the igneous rocks of 

 Goblin Combe. It varies much in coarseness and in the proportion 

 of oolitic grains present. Angular grains of quartz are always 

 plentiful. The lapilli are of two chief varieties : (1) a highly- 

 vesicular, glassy rock, which sometimes shows green palagonitic 

 alteration, sometimes is so loaded with ferric oxide that nothing 

 can be seen except the vesicles ; (2) a basalt with felspar-laths, 

 patches of serpentine or chlorite, and peroxidized magnetite-rods — 

 resembling, in fact, the lava of the western end of the Combe. 



(3) Summary of the Characters of the Tuffs. 



They are all highly calcareous, and most are best described as 

 ashy limestones. The proportion of lapilli is very variable. In 

 some rocks, such as those from the western Goblin-Combe exposure 

 and some of those from the eastern, lapilli form less, perhaps, than 

 a hundredth part of the material. In others, such as some of those 

 from Woodspring and from the eastern Goblin-Combe exposure, 

 they form more than one-third. While, in some districts (as is well 

 known) many of the lava-fragments in the tuffs are of a quite 

 different type from the lavas which flowed on the surface, that is 

 not the case with regard to this district, as all the lapilli are basaltic 

 in character, like the lavas. At Spring Cove and the western 

 exposure of Goblin Combe the lapilli consist of the same type of 

 basalt as the associated lava. At Woodspring they are, as a rule, 

 of a green, highly-vesicular rock, like a basaltic pumice. In the ash 

 from the eastern end of Goblin Combe both types of lapillus are 

 represented. Attention has already been drawn to the abundant 

 quartz-grains of the Goblin-Combe rocks and to their frequently- 

 oolitic character. 



V. Conclusions. 



The observations described in this paper support the conclusions 

 reached by those previous writers who have indicated the existence 

 of a volcanic episode in Lower Carboniferous times within the 

 Bristol district. They render it probable that the 'trap* of Uphill 

 and near Cadbury Camp is a product of contemporaneous volcanic 

 action. They have somewhat extended the number of recorded 

 localities in which lava or tuff is exposed. They establish the fact 

 that in all cases the lavas are basaltic in type, and that the lapilli 

 found in the adjacent beds are of the same basaltic character. 

 And they show that the volcanic episode in all cases occurred 

 during the deposition of the upper part of the Zaplirentis-\>e(is, 

 and before the strata characterized by Chonetes and Streptorhynchm 

 were deposited. 



