SoLLAS — On a Fragment of Garnet Sornfels. 51 



sometimes rudely parallel to tlie sides of the section, indicating 

 imperfect rhombohedral cleavage, sometimes quite indefinite in 

 direction. When two garnets touch one another very numerous 

 cracks start from the place of contact, breaking the crystals into 

 an infinity of fragments. Fracturing frequently occurs without 

 noticeable dislocation, but occasionally cases may be met with in 

 which the fragments of an originally single crystal have become 

 separated from each other by a considerable interval, which is 

 now filled up with the other constituents of the rock, most fre- 

 quently secondary quartz. This clearly proves that the garnets 

 had crystallized out before the cessation of the earth movements 

 which produced the schistosity of the rock, possibly before their 

 commencement. 



Compared with the fragments which compose the quartz- 

 felspar mosaic of the greater part of the rock the garnets are of 

 large size. They range from 0-18 to 0-016 mm. in diameter, while 

 the quartz and felspar fragments are seldom more than 0*009 to 

 0*014 mm. in length. Thus one of the larger garnets covers an 

 area large enough to include over a hundred of the quartz and 

 felspar fragments, yet neither these minerals nor mica ever occur 

 as recognizable inclusions in the garnet. In one or two instances 

 I have observed a fragment of quartz in the very middle of what 

 had the appearance of being a crystal of garnet ; but on closer 

 examination this seemed to be not one but several garnets which 

 had grown together, leaving the quartz in the middle. If the 

 quartz and felspar were already differentiated previous to the 

 development of the garnets, it is curious that we do not find them 

 as inclusions, and we are led to suppose either that they were 

 " eaten up " by the growth of the garnets or pushed on one side. 

 The mica very frequently " runs at " the garnet, so to speak, but 

 ends abruptly against it, without penetrating to the interior. In- 

 clusions — but of a different nature — are, however, far from absent. 

 Most of the sections are crowded with foreign particles of one 

 kind or another — minute rods, with straight parallel sides and 

 undetermined but crystalline terminations, frequently occur run- 

 ning parallel to one or more sides of the section. Sometimes 

 these acquire a comparatively large size, and are readily recog- 

 nised as prisms : they are colourless and transparent, doubly 

 refractive, but not dichroic ; they extinguish parallel to the sides 



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