J. M. Clements — Study of Contact Metamorphism. 91 



Cause of Chemical and Mlneralogical Changes in the Hocks 



described. 



The changes which have taken place in sedimentary rocks as 

 the result of contact with igneous rocks have given rise to a 

 great deal of discussion. The one school, notably represented 

 by the French geologists, contends that there is an actual 

 transfer of material from the igneous rock to the rock intruded 

 with more or less complete resorption of the latter; whereas 

 the other school has maintained that the indisputable meta- 

 morphism observed in such cases is due chiefly to the action of 

 the so-called mineralizers. Studies upon a series of contact 

 rocks similar to those here presented have given foundation for 

 the view upheld by Roth,* Zirkel,f and others, that in the case of 

 contact metamorphism produced by basic rocks an actual trans- 

 ference takes place. This view has been recently very strongly 

 advocated by W. Maynard Hutchings,;): who has described 

 some interesting products, which result from the contact of the 

 Whin Sill, which still further support it. 



The very considerable changes which are shown by the 

 above analyses to have taken place in the metamorphism of the 

 slates, especially the change in the amount of silica and 

 soda resulting in the production of albite in large quantity, 

 seem to add weight to the supposition that in such contacts 

 an actual transfer of material, possibly in the form, as has 

 been suggested by others, of a soda silicate, does take place 

 from the basic igneous rock to the intruded slate. 



Madison, Wis. 



* Chemische Geologie, by J. Roth: Berlin, 1890, vol. iii, p. 145. 



f Lehrbuch der Petrographie, by F. Zirkel: Leipzig, 2d edit , vol. ii, 1894, p. 722. 



% Notes on the composition of clay-slates, etc., and on some points in their 

 contact metamorphism, by W. M. Hutchings: Ueol. Magazine, vol. i, dec. 4, 1894, 

 p. 75. 



An interesting contact rock, with notes on contact metamorphism, by W. M. 

 Hutchings: Geol. Mag, vol. ii, dec. 4, 1895, p. 122-131, 163-169. 



