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Published online by Cambridge University Press: 01 May 2009
Amongst the rocks whose original structures have been more or less deformed by metamorpbic agencies the geologist very commonly meets with curious eye-like inclusions of mineral matter, which are generally known by the name of augen. Close investigation of a large series of rocks exhibiting these eyes brings to light the fact that under this name are classed two essentially different kinds of structure. in the one, the kernels or eyes are manifestly the unsheared portions of the rock, whose sheared portions constitute the schist that envelops the eyes. in the other kind of augen structure the eyes consist of crystalline minerals, whose development as such is shewn to be posterior to the shearing to which the matrix has been reduced, by the fact that the eyes of crystalline matter have not participated in the shearing, but are bright and generally unfractured throughout.
This is substantially part of a Lecture on the “Causes of Volcanic Action,” delivered under the auspices of the Royal Scottish Geographical Society at Edinburgh, December, 1892.
1 This is substantially part of a Lecture on the “Causes of Volcanic Action,” delivered under the auspices of the Royal Scottish Geographical Society at Edinburgh, December, 1892.
