J, M. Clements — Study of Contact Metamorphism. 83 



believed that they can vitiate the conclusion concerning the 

 effect of the metamorphic action upon the slates. 



In the further discussion, therefore, it is assumed that the note- 

 worthy differences between the rocks to be described are due to 

 metamorphic action, and are not due to the original chemical 

 differences. This assumption seems to be warranted by the fact 

 that the changes are in perfect accord with those described 

 from similar dolerite-slate contact zones in other areas. 



The products of the contact metamorphism are those banded 

 and spotted rocks which have been called spilosites, desmosites, 

 and adinoles, and they will be the special subject of this article. 



The dolerites (diabases) are coarse-grained, and do not exhibit 

 anything of especial interest, consequently no description will 

 be given of them. No evidence of any endomorphic action 

 whatever has been observed in them. 



In a study of contact action it is, of course, of the greatest 

 importance to be able to determine accurately the order of suc- 

 cession from the unmetamorphosed to the most metamorphosed 

 forms of the rocks. In the present case it is impossible to com- 

 pare sections from, or analyses of, any given stratum of the rock at 

 successive stages of approach to the line of contact, for the reason 

 that, where the exposures were found, the dolerite had been in- 

 truded parallel to the strike of the slates. Moreover, the exposures 

 -are very poor, indeed. This order of succession has, however, 

 been made out so satisfactorily for other localities by Lossen 

 and others, and the characters of each rock in the succession 

 have been so well described, that I have no hesitation, after 

 microscopical study of thin sections of the specimens, in pre 1 

 senting the series in the following order. Beginning with the 

 clay-slate, the least metamorphosed rock in the district, and 

 the ones farthest removed from the intrusives, we pass to the 

 phyllites, then to the spilosites and desmosites, and finally to 

 those which are known as adinoles, the latter being those which 

 occur next to the intrusive. 



The Clay-slates. 

 These are dull and lusterless banded rocks, ranging in color 

 from black to olive-green and red. They are usually impreg- 

 nated with more or less iron pyrites in large macroscopical 

 crystals. By high power, one can very readily distinguish in 

 the slates round or oval areas of limpid quartz, surrounded by a 

 dark grayish mass, which consists of minute flakes of white 

 mica, crystals of rutile, and some of hematite, here and there a 

 long, transversely-fractured, greenish needle, taken for actino- 

 lite, and, lastly, a dark grayish to black granular aggregate, 

 which is the chief coloring matter of the slate, and which 

 makes up a very considerable part of the rock. This aggre- 



