22 COKCRETIONAEY PATCHES AND FRAGMENTS IN GRANITE. 



Mr. Ormerod said he had observed these inclusions on the eastern 

 side of Dartmoor; there the inclusions were generally oval, and 

 called "mare's eggs," and the phenomena agreed with those de- 

 scribed by Mr. Phillips. 



Prof. Eamsat said these inclusions might be seen remarkably well 

 on the steps of the Duke- of- York's column. The subject appeared 

 to him to have been admirably worked out by Mr. Phillips. He 

 thought, however, that Mr. Phillips's remarks were not inconsistent 

 with the idea that some granites were metamorphic. 



Mr. W. W. Smyth congratulated the author of the paper, with 

 whom he heartily agreed. There were many cases to be seen in 

 Cornwall of fragments torn off from the neighbouring rocks. When, 

 however, you find aggregates, as of schorl, like balls, they must be 

 due to some kind of concretionary action. The Elba granites showed 

 a tendency to aggregation with schorl and with mica. 



Prof. Seeley quoted cases from the internal structure of crystals 

 of augite and hornblende of the Siebengebirge, where similar con- 

 cretionary masses occur plentifully in the trachytic rocks. They 

 generally have angular sides, as though large felspar masses had 

 been altered and removed. They are mostly rich in augite, are 

 often limited by a film of kaolin, and are quite as large as those in 

 granite. He thought they were analogous to septarian concretions 

 in clay, and due to the percolation of water removing materials from 

 one place and putting them down in another. 



Prof. JuDD said Mr. Phillips had undoubtedly proved that there 

 are two kinds of these enclosures in granite. He suggested that a 

 third class might exist, namely, fragments brought up from below, 

 like the nodules composed of augite, olivine, and enstatite, which 

 are found in so many basic rocks. 



Mr. Baiterman thought that no great dependence could be placed 

 upon external contour as evidence of the local or foreign origin of 

 an included mass, as in graphic granite the quartz might take the 

 angles of the felspar or might be freely developed ; then the rounded 

 form of olivine masses might be due to interrupted development, and 

 not to their being included fragments. He exhibited a piece of 

 zircon syenite from Labrador ; in it was a fragment, as it seems, of 

 a hornblende and soda-lime felspar rock, which, on the other side, 

 took a true crystal form of hornblende. 



Dr. Hiczs stated that spheno was common in the hornblende 

 gneisses of Scotland. He had observed many cases similar to those 

 described by Mr. Phillips, where the surrounding rock and included 

 fragments were identical, and where there was but little alteration 

 produced by the intrusion. 



Mr. Phillips thought the disappearance of rounded fragments on 

 sinking deeper in the rock, referred to hj Mr. Attwood, was only an 

 accident. He had found concretionary inclusions at all distances 

 from junction-surfaces. He thought that fragments coming up from 

 below, as referred to by Prof. Judd, would generally be dissolved or 

 greatly diminished in size during their passage. 



