C. H. Warren — Miner alogical Notes. 339 



appearance is illustrated by figs. 1 and 2. The outlines of each 

 layer are marked by extremely thin but distinct shells, in many 

 instances also curiously corroded, which represent the more 

 refractory upper surface of each layer. The distances between 

 such shells indicate a thickness for the original layers of from 

 0-2 to 1-5™^. 



Associated with the quartz and calcite, and evidently of the 

 same age, is a little reddish sphalerite and minute crystals of 

 iron pyrite. (Iron pyrite also occurs abundantly in the wall of 

 the pocket.) In a. vein of quartz traversing one specimen, 

 extremely minute, gray prismatic crystals of arsenic are embed- 

 ded, and on the reniform surface of the same specimen can be 

 seen a light gray druse of arsenic. This arsenic is clearly of 

 the same age as the quartz and indicates that the same solu- 

 tions which deposited the quartz were carrying some arsenic, 

 evidently derived directly from the reniform masses. 



Careful qualitative tests showed the presence of a small 

 amount of antimony and a trace of sulphur in the arsenic. 



E". ^. Evans,* in a recent description of native arsenic from 

 a vein traversing a nepheline-syenite rock in the vicinity of 

 Montreal, attributes its formation there to deposition by fuma- 

 role action. It is believed that a similar method of formation 

 obtained for the Arizona arsenic. Gaseous emanations, carry- 

 ing some volatile arsenic compound, may very probably have 

 escaped from underlying igneous rocks into a pocket in the 

 limestone, and finding there, as suggested by Professor Crosby, 

 a local relief of pressure, decomposed and deposited successive 

 layers, eventually forming the reniform masses. After their 

 formation these were fissured to some extent by shrinking but 

 chiefly through movements connected with the faulting. Sub- 

 sequently, solutions carrying silica, carbonate of lime, and a 

 small amount of sulphides removed a portion of the arsenic 

 and deposited the minerals named. 



The author is indebted to Mr. John L. Gardner of Boston 

 for the very excellent photographs from which the present fig- 

 ures were taken. 



II. Anthophyllite with the Fayalite from Rochport, Mass. 



During the fall of 1902 a mineral was submitted to the 

 author for identification by Messrs. F. W. Horton and Cutler 

 D. Knowlton, students in the Massachusetts Institute of Tech- 

 nology. The mineral was found by them in the quarries of 

 the Kockport Granite Co. at Kockport, Mass., and proved to 

 be fayalite, the first occurrence of which was described by 

 Penfield and Forbes^f who analyzed it and established the 

 optical constants for the species. 



* This Journal (4), xv, 92. f This Journal (4), i, 129. 



