VOLCAIs^IC EOCKS OF DAETMOOR. 295 



might come from resistance of hard amygdaloids, cleavage, alteration 

 of a fluidal structure, and deposit on a fissile face. He thought, 

 perhaps, the last the most probable explanation in this case, as 

 the cavities did not appear materially crushed. 



Prof. Maskelt]s'e said that a spongy lava saturated with water 

 which had no exit would not necessarily crush. 



llr. Baitee^ian agreed that these rocks were small lava-flows 

 interstratified with shales. He compared these Brent-Tor rocks 

 with the Nassau Schalstein. 



Mr. J. A. Phillips said that analyses of this rock showed that 

 the lime in the carbonate of lime had been derived from felspars. 

 He exhibited a specimen of ISTassau Schalstein. Cornish Schalstein 

 contained -64 per cent, of phosphoric acid ; that from ^Nassau 

 •57 per cent. Staffelite occurred below the !N"assau Schalstein. 



The AiTTHOB thought that Mr. Thorpe's specimen was not a vol- 

 canic, but a calcareous tufa. He thought the schistose structure due 

 to the elongated vesicles, so that the rock split along the planes of 

 least resistance. Prof. Maskelyne's suggestion was well worthy of 

 consideration. 



