114 Wells and Penfeld — Herder ite from Maine. 



of quartz, sheared micas and recognizable fragments of plagio- 

 clase in the midst of decomposition material furnished by 

 them. As the fault was in a different kind of rock from the 

 shear-zones in norite, its products are somewhat different, and 

 the great proportion of hydrated silicates give the impression 

 that the shear-zones earlier described may be the result of a 

 secondary metamorphism which the one at Hammondville has 

 not experienced. This fault broke the ore and drill holes have 

 failed to find it again. Experience in mining the adjacent 

 Penfield bed has shown that the ore is cut off where the work- 

 ings extend under a neighboring gully, and suggests that these 

 topographical features are due in instances at least to faults. 

 Such an explanation has proved true in many regions else- 

 where* and will probably be applicable to some valleys of 

 large size in the Adirondacks. 



Crushed strips along faults are well known in mining dis- 

 tricts and have often furnished the receptacles for ores, as at 

 Butte, Montana, f The drift of modern opinion refers to them 

 an increasing number of so-called fissure veins. Where condi- 

 tions are unfavorable for vein formation dynamic metamor- 

 phism results. The work of Lossen, G. H. Williams, Teall 

 and many others has shown the widespread effects of dynamic 

 metamorphism, but a somewhat careful review has failed to 

 reveal descriptions of any instances of such restricted effect 

 and such mineralogical results as are exhibited on Avalanche 

 Lake. 



Geological Laboratory, Columbia College. 



Art. XYI. — On Herderite from Hebron, Maine ; by H. 

 L. Wells and S. L. Penfield. 



During the summer of 1891 we received from Mr. L. Iv. 

 Stone of Paris, Maine, a small mineral, specimen for identifica- 

 tion. The unknown mineral consisted of a few yellowish 

 white crystals on albite. They were about 3-5 mm in length and 

 their total weight probably did not exceed 2 or 3 grams. Mr. 

 Stone stated that this was the only specimen of the mineral 

 that had been found, and that it was discovered in 1890 at the 

 pollucite locality in Hebron. 



A preliminary examination proved that the mineral was a 

 phosphate, very slowly soluble in hydrochloric acid and yield- 



* J. H. Einaban, Talleys and tbeir Relations to Fissures, Fractures and Faults. 

 London : Trubner & Co. 



f S. F. Emmons, Notes on tbe Geology of Butte, Trans. Inst. Min. Eug., July, 

 1887, and Structural Relations of Ore Deposits, idem, xvi, 804. 



