THE SOUTHERN COMPLEX. 123 



A 8Uininaiy of the more iiuportaut cliaractcrs ot' the granites and grani- 

 toid gneisses is here given. An alkaHne feldspar is always the chief con- 

 stitnent, while in the majority of cases it composes three-fotn'ths or more of 

 the rocks. Moreover, a very large proportion i>f tliis feldspar is of the species 

 orthoclase, althongh microcline and acid plagioclase are always present and 

 often plentifulh'. Tlu^-e is a very marked tendency in these feldspars 

 to idiomorphic forms. In some cases in which the felds|»ar is predomi- 

 nant this tendency is so strong that the rock might be tlescribed as panidio- 

 morphic. This characteristic of the granites and syenites is shown both in 

 hand specimen and in thin section. Qnartz varies in cjnantity to an amount 

 about equal to that of the feldspar. When the quartz is not plentiful it is 

 in part so arranged with reference to the feldspar as to suggest that it might 

 be of secondary origin. This suggestion is reinforced by the fact that occa- 

 sionally the feldspars near their exteriors contain saturating quartz. This 

 pegmatitic structure ma^■ be due, however, to the sinmltaneous crystalliza- 

 tion of quartz in the final stages of the formation of the feldspar. 



Further, it does not appear jjrobable that all the quartz found in these 

 rocks is a secondary product, for in the most acid of them the feldspar and 

 quartz interlock in the irregular fashion characteristic of ordinary granites. 

 In the massive granites the onh' other inqiortant constituents are horn- 

 blende, biotite, and chlorite. The hornblende (piite often occurs in well 

 defined crystals. The chlorite frequently imitates the forms of the horn- 

 blende. The l)iotite is in well developed, sharply outlined l)lades. These 

 minerals are ftrdinarily between the feldspars, but bear such relation to 

 them as to suggest that the feldspars have adapted their forms to these 

 minerals rather than the reverse. Not infrequently each of them is include<I 

 in large blades or crystals in the feldspar. It follows from these relations 

 that the hornblende and biotite were earlier than the feldspar, or else that 

 these minerals have developed subsequently to the consolidation of the rock. 



The most important fact developed by the study of the .Southern 

 Complex is the apparent gradual change between the massive rocks and the 

 schistose ones. These gradations have already been alluded ti >. It will, then, 

 here only be necessary to remember that the lines separating the granites and 

 the gneissoid granites from the fine grained gneisses and schists are more 



