392 ORIGIN OP NOVACTTLITES AND QTJARTZITES. [Aug. 1 894, 



they mighb have had an organic derivation. Moreover, in the beds 

 of Carboniferous chert from Ireland, Belgium, Yorkshire, Wales, 

 etc., and in the cherts of the Durness Limestones (sections of which 

 were exhibited), there were numerous rhombohedral crystals of 

 calcite, the same as in the novaculites, and they also resembled these 

 in other respects. As these cherts had been proved to be derived 

 from the siliceous remains of sponges, it might well be supposed 

 that the silica of the novaculites had a similar origin. It was true 

 that no siliceous organisms had as yet been found in the novaculites, 

 but this might arise from imperfect observation, or it might be that 

 the changes which had taken place in the rocks had obliterated 

 them. 



Prof. Hull remarked that the chert-beds of the Upper Car- 

 boniferous Limestone of Ireland, referred to by the Author, and 

 described in the joint memoir by the late Mr. Hardman and 

 himself, were composed of variable proportions of carbonate of lime 

 and silica, and also contained silicified shells, corals, and crinoids — 

 animal structures that must primarily have been formed in carbonate 

 of lime : thus proving that the rock had originally been to a great 

 extent a limestone. Along with these structures were numerous 

 spicules of siliceous sponges, recognized in the thin slides by 

 Dr. Hinde. But the rock described by the present Author, so far 

 as he had been able to gather, was of quite a different character 

 from these Carboniferous chert-beds. It was a solid quartzite, 

 without evidences of having contained marine calcareous organisms; 

 and however ingeniously the Author had succeeded in showing, by 

 means of his researches in the laboratory, that a limestone might 

 be changed into a quartzite, he (the speaker) feared that without 

 some better evidence of so remarkable and fundamental a change in 

 the composition of the Arkansas rock described, Mr. Butley's views 

 could scarcely be accepted. 



The Author, in reply to Dr. Hinde's remarks, stated that he had 

 purposely refrained from expressing any opinion concerning the 

 source from which the silica of the novaculites had been derived. 

 Dr. Hinde was doubtless correct in assuming that the silica of chert 

 was frequently composed, at least in part, of the remains of sponges. 

 He had not detected any sponge-spicules in either Arkansas stone 

 or Ouachita stone. He also briefly alluded to the observations of 

 Prof. Hull. 



