Vol. 60. 1 IGNEOUS ROCKS AT SPRING COVE. 100' 



Discussion. 



The Chairman (Sir Archibald Geikte) remarked that, since the 

 publication of the joint description with Mr. Strahan, referred to 

 by the Author, he had had an opportunity of re-examining the fine 

 series of intercalated lavas in the Carboniferous Series of Fife. In 

 most, if not in all, of those basalts which show the pillow-structure 

 the materials that now fill up the interspaces between the ellipsoids 

 have come from above and evidently belong to the series of sedi- 

 ments — tuff, sandstone, shale, limestone, etc. — which followed the 

 emission of the lava. There is no trace of an explosive character 

 in the lavas themselves ; and he greatly doubted the possibility of 

 a lava which had once escaped from the vent and flowed for some 

 distance, subsequently blowing itself to pieces by the expansion of 

 its own imprisoned vapours. No doubt, sudden contact with water 

 might cause some lavas to break up ; yet it was nevertheless the fact 

 that in the case of those in question, though they had all flowed 

 out over the bottom of a lagoon or the floor of the more open sea, 

 none of them showed more than the usual irregular cracked surfaces. 

 He did not think that there was ever much resemblance between the 

 behaviour of a sill and that of a submarine lava-flow. He welcomed 

 the additional information now supplied regarding an exceedingly- 

 interesting little volcanic district, and hoped that the Author might 

 be induced to study the other exposures iii the same careful and 

 detailed manner. 



Prof. Watts remarked that the paper constituted a very important 

 contribution to volcanic geology. It enabled us to realize that con- 

 ditions of vulcanicity prevailed in Carboniferous times similar to the 

 vulcanicity of the present day. He was greatly impressed with 

 the suggestion that the eruption described in the paper was of the 

 Pelean type : the lava was blown to atoms, and the pulverized material 

 formed a fluxion-tuff. In the Llandeilo of the Shelve district the 

 speaker had formerly been perplexed how to classify a rock similar 

 to that described by the Author. There was no reason why lava 

 should not be blown to dust beneath the sea as well as on land, and 

 the pressure of the water would induce conditions reminiscent of 

 an intrusive sill. The Author had satisfactorily proved that most 

 of the sedimentary material caught up in the lava had been derived 

 from below, and his evidence was not inconsistent with that brought 

 forward by the Geological Survey from the Southern Uplands of 

 Scotland. 



The Author thanked the Fellows for their reception of the paper. 

 He quite agreed with the Chairman that limestone, and sedimentary 

 material generally, found within the body of pillowy lavas, might 

 have come about in different ways in different cases, and that in 

 some cases the material had doubtless come from above, either in 

 solution or as sediment; but, from the evidence at Weston, it appeared 

 certain that it might have come from below, ejected from the vent 

 or picked up by the moving lava from the sea-floor. He did not 

 think that it was necessary to assume a great depth of water at 

 Weston during the outpouring of the lava. 



