Yol. 69.] VOLCANIC EOCKS OF THE FOBFAESniEE COAST. 483 



torrent-action. How did the Author explain the occurrence of the 

 sedimentary material in the interstices of the lava ? Was it washed 

 in by the water of a lake, or by rain-water, or was it the result of 

 «eolian action? The suggestion that .cavities were formed by steam 

 in sedimentary rocks below a lava-flow was very valuable. 



Dr. J. V. Elsden remarked on the petrographical interest of the 

 paper. Some of the rock-types appeared to be rich in magnesia, 

 and the augites might be expected to show the basal striation 

 characteristic of such rocks in other areas. He asked whether 

 these various rock-types occurred in separate lava-flows,- or in 

 •different parts of the same flow. The character of the phenocrysts 

 suggested an origin from a differentiated magma-basin. It would 

 be interesting to know what kind of rocks marked the dyke-pbase 

 •of these eruptions. 



The Authob thanked the Fellows for their kind reception of his 

 paper. In reply to Dr. Evans, he said that true conglomerates, 

 indicating the action of strong currents, are occasionally interbedded 

 with the lavas. The fragments of slaggy lava cemented by line 

 sediment are found at the surface of almost every lava-flow, and 

 were probably produced simultaneously with the lava below. He 

 stated, in reply to Dr. Elsden, that each of the types of volcanic 

 rock mentioned generally includes several sheets of lava. None of 

 the augite-crystals show basal striation. The few dykes consist 

 of much -weathered rock, less basic than the lavas, no olivine and 

 very little pyroxene being present. 



