182 



University of California. 



[Vol. r. 



vicinity of Berkeley this blue amphibole was found to be abundantly 

 present, and quite characteristic of these rocks, and it was thought 

 desirable to make a detailed investigation of the petrographical 

 character of one of its occurrences. For this purpose a rock was 

 selected which contained the mineral in unusually well-developed 

 crystals, quite readily separable from their matrix, and, therefore, 

 very favorably situated for study. The result of this investiga- 

 tion was to show that the mineral differed in so many essential 

 points from the other recognized members of the amphibole group 

 as to warrant its consideration as a new species. It is the purpose 

 of the present paper to present the characters of this new amphibole 

 together with a description of the rock in which it was found, the 

 latter being of a quite unique character. 



THE ROCK. 



The rock in question was found as a large boulder in the bed 

 of a small stream, draining from the west slope of the Contra Costa 

 Hills, about three miles north of Berkeley. Repeated search failed 

 to reveal with certainty the source of this boulder, but closely 

 similar rocks were found in the near vicinity, forming part of the 

 extensive schist complex of the region, and the size and position 

 of the boulder forbid the belief that it had other than a local origin. 



Hand specimens of this rock show a distinctly schistose struc- 

 ture, owing to which it splits with great ease into flat slabs. The 

 surface of such a slab is shown in the photograph, Plate 10. On 

 the surface are seen numerous columnar crystals of the dark blue 

 amphibole, embedded in a milk-white granular matrix, which has 

 much the appearance and structure of granulated sugar, and readily 

 crushes to a crystalline powder under the hammer. Minute specks 

 of a pale yellow color are seen abundantly in the matrix. Trav- 

 ersing the boulder in many directions are veins from \ to fa of 

 an inch in width, composed of a pale green mineral, coarse granular, 

 with perfect cleavage, and the hardness of feldspar. Where these 

 veins intersect the amphibole crystals, the broken ends of the latter 

 are frequently seen to be connected across the vein by a band of 

 pale green fibrous material which also forms isolated fibrous aggre- 

 gates in the vein matter. 



