228 GEOLOGY. 



theory of their origin is concerned. The same old arguments of the 

 metamori^hism of sediments are advanced, and they are met by the 

 same objections. One would frequently be tempted to think, on read- 

 ing treatises that deal with this subject, that the matter was clearly and 

 well understood, yet there still remain many able scholars to whom "the 

 crystalline schists remain," as Inostranzeflf says, " lithological hiero- 

 glyphics." 



Moreover, the study of the rocks themselves has been in a backward 

 state. Lithologists have now for years been very busy investigating 

 the eruptive rocks, and the result is that volumes of interesting infor- 

 mation concerning their nature and composition have been issued, and 

 a system of classification devised, which, if not satisfactory to all, is at 

 least suited to the wants of the time. IsTo very systematic work has 

 thus far been attempted on the schists, and the subject is in a rather 

 chaotic condition. Yet it can be said that more studies have been made 

 on local groups of schists during the past two years than ever before, 

 and many new and interesting varieties have been found, and many facts 

 accumulated for future systematization. The following circumstances 

 may be considered as interesting, and may indicate the character of the 

 work performed. 



Olivine has been shown to be a constituent of some hornblende 

 schists by Kalkowsky, and a great group of stratified olivine rocks, 

 which occur in Sweden, have been shown by Reusch, and afterward by 

 Brogger, to belong to the crystalline schists. The time was when oU- 

 vine was considered as especially characteristic of eruptive rocks, but it 

 may be considered that it is very far from being confined to this group. 



The very abundant occurrence of rutile in the schists has been shown 

 by several writers, notably by Sauer. This has provoked much discus- 

 sion, since some minerals, previously referred to Zircon, are probably of 

 Tutile. Zircon is, however, sometimes a constituent of the schists. Mr. 

 van Werveke thinks the heart-shai^ed crystals in the whetstone schists 

 may be of rutile. 



It has often been assumed that the rocks composed of triclinic feld- 

 spar with members of the pyroxene and hornblende group were mostly 

 eruptive. Even plainly stratified rocks of this kind have been con- 

 sidered as lava overflows or tufts. Many studies have been made 

 in the period under consideration which show that such rocks occur 

 abundantly among the stratified schists. Benecke and Cohen describe 

 such in the neighborhood of Heidelberg, and Rolle a whole series of such 

 from the Rhiitic Alps. Fouque and Levy describe such under the name 

 of Amphibolite gneiss; Stelzner such from Lapland, and yet many 

 others have been mentioned. It will be remembered that this is a sub- 

 ject in which Professors Hunt and Dana have in times past taken much 

 interest, and the group of crystalline schists is now generally regarded 

 as including rocks of this class. This is an advance. 



Several efforts, notably by A. Sauer, have been made to show that 



