PECULIAR >riNi:ilAL TIlANSFOllMATIONS. 473 



tweeii the formation of the inaiu mass and the injection of this last variety, for we 

 find this luie red «rranite widely scattered over the entire area, and we ilnd it to 

 be more recent than the tlevelopnient of "aniren'Mn the coarser mass. Though 

 later, it must have assumed its place Ion;; prior to the advent of Paleozoic time, 

 since it occui"s nuich metamorphosed under the unchan^^ed sediments of the Silurian 

 and possibly the Camljrian. 



Conclusions 



We find, then, in (his area .^ood illustrations of coarse anil line grained unanular, 

 hypidiomorphic irranular, porphyritic ujranular to jiorphyritic microt^ranitic and 

 panidiomorphic granular structures, each of which characterizes a sharply delined 

 tyt>e of a sinjxle cycle in which we find but one mineralogic type developed. Be- 

 sides, should we consider secondary structures we should find all of the variations 

 in the development of *'au<i:en" and of gneisses, as well as many of the peculiar 

 features i)roduced in rock masses by the action of hot-si)rin<^ and mineralizin<j: 

 agencies. 



Mr Mathews' paper was discussed by J. l\ Iddiiigs, J. E. Wolff, Whit- 

 man Cross and H. N\'. Turner. 



The chairman of the section presented the following, with exhibition 

 of the specimens : 



ILLUSTRATIONS OF PECULIAR MINERAL TRANSFORMATIONS 

 BY B. K. EMERSON 



CoMenis 



Page 



Serpentine pseudomorphs tifier olivine, formerly cnlled quartz psoii lomorphs 473 



Culcito pseiidotnorphs after salt in Triassie slialo 473 



Puckering of corundum crystals around alianite 474 



Serpentine Pseudomorimis afteu Omvine, formkuly calleo Quartz PsEUDOMoui'irs 



A specimen, presumably uniipie, was shown, having several large attiiched crys- 

 tils more than an inch long, showing the common forms of olivine now changed into 

 a pale yellow ser|)entine, clo.sely resembling the Snarum forms. The crystals have 

 long iK'en cited asrjuartz pseudomorphs from Middletield, but the locality has been 

 lost for many yeai-s. This si)ecimeu is from the collection of Mr .James Clark, 

 formerly of Brooklyn, an<l now belongs to Smith College. Its labfl states that the 

 locality was on the bnjok which crosses the great seri)entine bed in Middleiield, 

 and that it was ])urposely covered up by some one many years ago. 



Cai^citk Psr:ri)oM')iuM[s AirKit svi/r i\ Tkfass[c SiiArj-: 



A H|)ccimenof fine black shale of Triaasic age is covcMcd with white liius arranged 

 in triangles, cro.s.ses and lines, radiating from the' corners of small s(iuares. A 

 feathery outgrowth at times borders these lines. The material is calcite, and the 

 lines are tracings of the various chance crusa-sections of skelet<jn cubes, about 



