REACTION RIMS. 221 



The commonest reaction rims or zones of minerals elsewhere noted 

 have been around olivine and apparently due to its proximity to feldspar. 

 In this case we usually see next the olivine a rim of hypersthene granules, 

 outside of which is actinolite in radiating fibers, often with small spinels 

 entangled, and then the plagioclase. Various modifications of this suc- 

 cession have also been recorded, a brief review of which is given below.* 

 In the lake Champlain gabbros the following zones were noted around 

 olivine : Next the olivine is a zone of granular hypersthene, next quartz, 

 next garnet and then feldspar (slide 121), or we may have olivine, hyper- 

 sthene, brown hornblende, garnet, feldspar (slide 146). There may even 

 be nests of hypersthene bits, with garnet rims, the olivine having appar- 

 ently been exhausted. In the same specimen of rock (slide 146) the 

 slide shows also the ramifying branches and rods of pyroxene such as 

 were figured by W. S. Bayley j and regarded as original intergrowths. 

 They occur in great numbers in some of the writer's slides, almost form- 

 ing streams outward from the olivine. In the outcrop north of Port 

 Henry, along the lake shore, most interesting passages of the ophitic 

 gabbro into bands of thinly foliated, gneissoid structure can be traced. 

 This has doubtless been induced by pressure, and the gneissoid character 

 has been caused by the stretching of the dark silicates and of the feldspar 

 into elongated, parallel lenses. In such specimens brown hornblende 

 becomes especially prominent and replaces quite entirely the pyroxene. 

 It would appear to be secondar^^ Evidence of dynamic effects is every- 

 where present in the slides. 



*A. Olivine surrounded by successive zones of tremolite and actinolite. Tornebohm : in Swedish 

 hyperite. Neues Jahrbuch.,1877, p. 383. Lacroix : in gabbro of Pallet, France. Bull. Soc. Min. Fr., 

 vol. xii, 1889, p. 245. 



B. Olivine with successive zones of biotite and talc. Julien : Geol. of Wis., vol. iii, 1880, p. 235. 



C. Olivine with successive zones of anthophyllite and actinolite. Becke: in Austria and at Ross- 

 wein. Saxony. Tscher. Mitth., vol. iv, 1882, pp. 331, 450. Teall : at the Lizard, in England. Min. 

 Magazine, October, 1888, p. 116. 



D. Olivine with successive zones of hypersthene and actinolite. F. D. Adams : from the Saguenay 

 river, Canada. Am. Naturalist, November, 1885, p. 1087. T. G. Bonney : from Aberdeenshire. Geo!. 

 Magazine, October, 1885, p. 4.39. J. H. Hatch : from Madagascar. Quar. Jour. Geol. Soc, May, 1889, 

 p. 343. J. W. Judd : locality not stated. Jour. Chem. Soc. London, vol. Ivii, 1890, p. 423. W. D. 

 Matthew, gabbro near Saint John, New Brunswick. Trans. N. Y. Acad. Sci., April, 1894. Probably 

 the cases cited by G. H. Williams of olivine, colorless pyroxene and actinolite belong here. Balti- 

 more gabbros. Bull. 28, U. S. Geol. Survey, 1886, p. 52 ; Peekskill, N. Y., Am. Jour. Sci., January, 1886, 

 p. 35. 



E. Olivine with successive zones of hypersthene and garnet. Kemp, this contribution, 1893. 



F. Hypersthene with successive zones of actinolite and hornblende. G. H. Williams: Baltimore 

 gabbros. Bull. 28, U. S. Geol. Survey, 1886, p. 42. 



G. Titaniferous magnetite surrounded by successive zones of biotite, brown hornblende, garnet. 

 Lacroix : at Odegarden, Norway. Bull. Soc. Min. Fr., vol. xii, 1889, p. 232. Kemp, this contribution, 

 1893; also with zone of quartz. 



Other zones like the " kelyphite " arotwid garnet are not mentioned here, as they have no direct 

 connection with this paper. 



tW. S. Bayley: Fibrous Intergrowths of Augite and Plagioclase In a Minnesota Gabbro. Am. 

 Jour. Sci., June, 1892, p. 515. 



XXX— Bur,[,. Geol Soc, Am., Vol. 5. 1893. 



