CONTACT METAMOKPHISM BY INTEUSIVES. 211 



trary, about 12 times as much soda as there was m the slate has been added 

 to the contact rock. This causes a reversal of the relations of the soda and 

 potassa, so that, whereas in the clay slate there is present 10 times as much 

 potassa as soda, we find in the contact rock taken as a sample very nearly 

 10 times as much soda as potassa. The very considerable change in chemi- 

 cal composition, especially in the amount of silica and soda, seems to lend 

 great weight to the supposition that in such contacts an actual transfer of 

 material (soda-silicate) takes place from the basic intrusive to the slate. 

 This idea is upheld by Roth,^ Zirkel,^ and others. W. Maynard Hutchings^ 

 advocates this view, and has described some interesting products as a result 

 of the contact of the "Whin Sill which still further support it. 



NO ENDOMOKPHIC EFFECTS OF DOLERITE INTRUSION. 



Although the exomorphic contact effects of the dolerite intrusion were 

 so obvious, no evidence is found that the dolerite itself suffered any change 

 consequent upon its intrusion. 



METABASALT. 



Basalt has been described at length under the volcanics, where it plays 

 an exceedingly important role. Basalt as a dike has been found in only 

 two places, and therefore very little remains to be added. 



The two basalt dikes occur within a very short distance of each other, 

 in sees. 15 and 16, T. 42 N., R. 31 W., and are found ^penetrating- the crystal- 

 line schists of the Upper Huronian. Their relations to the other intrusive 

 rocks of the same region are not known. They are probably of the same age 

 as the dolerites, of which they should most likely be considered offshoots. 



These dikes are a porphyritic basalt. The phenocrysts were of augite, 

 olivine, and labradorite. They were in a ver}^ fine groundmass of feldspar, 

 augite, and iron oxide. However, the former existence of the augite and 

 olivine phenocrysts is determinable only by means of their outlines. They 

 are in very small quantity and are entirely altered to pilite. The feldspar 

 phenocrysts are in coarse, heavy crystals and are remarkably fresh. The 

 groundmass is very fine grained, and ranges from an exceedingly fine micro- 



' Chem. Geol., by J. Roth, Berlin, 1890, Vol. Ill, p. 145. 



= Lehrbuch tier Petrographie, by F. Zirkel, Vol. II, 1894, p. 722. 



•■' Notes on the compositiou of clay slates, etc., and on some points in their contact metamorphism, 

 by W. Maynard Hutchings: Geol. Mag., Vol. I, Dec. 4, 1894, p. 75. Chem. Geol., Vol. Ill, p. 145. An 

 interesting contact rock, with notes ou contact metamorphism, by W. Maynard Hutchings : Geol. Mag., 

 Vol. II, 1895, pp. 122-131, 163-169. 



