168 The American Naturalist. (February, 
been affected near the contact with the granite. Green hornblende, 
brown mica, colorless pyroxene, epidote and sphene are the most con- 
spicuous new minerals formed. These lie ina clear, granular mosaic, 
which may consist of newly developed quartz and feldspar. The com- 
ponents of the vesicles have in most cases given rise to a mixture of 
hornblende and quartz, but in other cases a little calcite may remain 
unaltered in the center of larger vesicles, while surrounding it are usu- 
ally hornblende, colorless pyroxene, quartz and epidote, and sometimes 
in addition, zonal garnets, sphene and a few other minerals. The 
feldspar found within the vesicles of metamorphiosed andesites is 
thought by the authors to be the result of the weathering of these rocks 
rather than a product of contact action. In concluding their paper 
some interesting thoughts are suggested as to the source of the materials 
producing contact minerals. It is known that limestones when pure 
may recrystallize as marbles without the production of contact miner- 
als, but that when impure the silica in the impurities may (and gener- 
ally does) release the carbonic acid and recrystallize with the calcium 
as silicates. In some of the vesicles of the rocks around the Shap gran- 
ite, however, the calcite has recrystallized, with the formation of sili- 
cates only around the edges of its mass, proving plainly that silica was 
obtained for the production of the silicates only by the calcite imme- 
diately in contact with the silicates. The conclusion is that in cases 
of thermometamorphism no transference of material takes place within 
the mass of the altered rocks except between closely adjacent points. 
In the production of the lime silicates studied, the interchange of lime 
and silica is estimated to be limited to a distance of zy of an inch. 
Other observations indicate the correctness of this conclusion." 
Petrographical News.—In the Obersweiler gneiss of north Voge 
sen are dykes of basic rocks that Andreae and Tenne’ identify 98 
hornblende kersantites. They consist of a panidiomorphic aggregate 
of plagioclase, green hornblende, a little mica, quartz, apatite, ee 
Other dykes of the region are quartz-melaphryes of the navite Ria 
The quartz is undoubtedly original. Its grains are much corroded 
the resorption rims around it are composed of augite and glass. © 
rock is interesting as the first recorded example of a dyke rook t 
ponding to the volcanic quartz-basalts. 
The porphyritic granite of northern Lausitz contains large eh 
bers of apatite crystals, sometimes as many as a hundred in & singlo 
"See also Journ. of. Geol., Vol. I, p. 574. 
* Zeits. d. deutsch. geol. Ges. 1892, p. 824 
