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The eccentric distribution of the deposits along some igneous contacts 

 is correlated with the presence or absence of fractures which could 

 serve as channels for the metamorphosing solutions, but other eccentrici- 

 ties such as the presence of chunks of unaltered limestone in the intrusive 

 are not readily explained. Where the intrusive rock is in contact with a 

 Wge body of sediments the contact-metamorphic rocks may follow the 

 contact rather regularly, or may replace certain beds in the sediments, 

 or may follow fissures crossing them. Unlike many contact-metamorphic 

 deposits which are notably compact, these commonly contain vugs 

 some of which attain the dimensions of caves in which a man can stand 

 upright. These are not the result of solvent action subsequent to 

 metamorphism but were formed during metamorphism, and are charac- 

 terized by crystals of quartz some of them a foot long projecting inward 

 from their walls. 



Contact metamorphism has usually affected the igneous rock as 

 well as the limestones, but the metamorphic zone is much narrower in 

 the intrusive than in the limestone and is much more siliceous being made 

 up mostly of quartz with subordinate dark silicates of the same varieties 

 that characterize the adjacent altered limestone. A distinct zoning is 

 usually perceptible in the alteration of the limestone. The zone nearest 

 the intrusive is characterized by dark-colored iron-bearing silicates — ■ 

 iron-bearing garnet, epidote, pyroxene, hornblende, etc., with calcite and 

 quartz and minor amounts of other minerals. This zone is the chief 

 host of the scheelite. 



Beyond this zone comes a zone characterized by light- colored sili- 

 cates poor in iron, tremolite and wallastonite being the commonest of these 

 silicates. Colorless diopside, scapolite, colorless garnet, and other silicates 

 are present in less abundance. Calcite is very abundant. Scheelite 

 is absent. The zone of light-colored silicates grades outward into the 

 marble that forms the outermost part of the contact-metamorphic aureole. 



Evidences are present that in many of the deposits the minerals were 

 not deposited contemporaneously, but that one mineral followed another 

 in a regular sequence. The details of the successive replacements were 

 not worked out microscopically, but in general it appears that garnet 

 was one of the first to be deposited and that sulphides were among 

 the last. 



The authors propose the name "tactite" for the rocks and ores de- 

 veloped by contact metamorphism nearest the intrusive (Latin, tactus, 

 "touch"). This term seems well chosen and may prove a convenience. 

 It should be noted that the authors designate as "tactite" only the zone 



