STRUCTURAL GEOLOGY. 35 



Tin- Kfkrquabie granite.] 



occupied by a fine interlocked secondary development of feldspar and quartz. The 

 margins of the feldspars frequently are interlocked in this new growth. As this fine 

 matrix increases in amount so the rock becomes porphyritic; as it increases in 

 coarseness so the rock becomes granitic, but in all cases, or in nearly all, there is a 

 distinct difference between the old feldspars and the new (compare rocks Nos. 1100 

 and 1101). Along with this generation of new feldspathic material is also the 

 recrystallization of the quartz, thus making a truly granitic rock. The old feldspars, 

 which, in the elastics proper, without metamorphism, have a tendency to disappear 

 by a process of micro-gran ulitization into a fine mesh of secondary feldspar and 

 quartz resembling the surrounding matrix, are by metamorphism regenerated by 

 new borders and by micro-granitic growths of coarser grain, and by these new 

 growths interlock about their margins. Occasionally the old feldspars embrace and 

 surround idiomorphic small crystals of augite, having taken that relation in the 

 magma in which they were generated, but the later feldspars do not enclose augite 

 in that way. When the fragmental augites are not altered to hornblende, which 

 alteration is usual, they are simply embraced between the newly developed feld- 

 spars. The old feldspars, as contrasted with the new, may be seen in Nos. 1046 and 

 1051. Indeed this distinction is observable with more or less certainty in nearly 

 every thin section examined. 



On a porphyry knob on the north side of the lake, at the corner of sees. 29, 30, 

 31 and 32, T. 65-6, there are, as observed in the field, transitions from the porphyry 

 to the schist at least to a green rock that contains the elements of the schist and 

 nearly the same micro-structure, but yet has a petrog-raphic alliance with the por- 

 phyry. Such intermediate rocks are found at several places, and in the field there is 

 no line of distinction, the transition taking place in a few feet. These intermediate 

 rocks of course have some origin. The microscope shows that the internal structures 

 and composition are in accord with the major structures. In one direction the char- 

 acters become more and more coarse and crystalline, and in the other more and 

 more clastic, without the introduction of any new minerals. It appears as if the 

 siliceous actinolite schist, losing locally its coarse feldspars, was converted into a 

 dense green rock of hornblende, biotite, quartz and feldspar, in one direction, and 

 in the other, with more or less preservation of the coarse feldspars that frequently 

 characterize it, the same force had generated a lot of coarser quartz and secondary feld- 

 spar, and thus cemented the original debris into a granitic rock. Throughout the 

 schist, even in its least metamorphic condition, there is a fine background of micro- 

 granulitic quartz or of quartz and feldspar (No. 1047), which is ready, in case of the 

 application of new forces, to take on new forms. The background matrix in the 

 porphyry, as in the granite, is the same fine interlocked quartz, or quartz and feld- 



