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University of California. 



[Vol. 2. 



masses which are probably derived from peridotite. Ledges of the 

 serpentine weather out into most fantastic forms, composed of a 

 porous, kaolin-like material, in which all evidences of the orig- 

 inal structure have been lost. They are not infrequently trav- 

 ersed by veins of quartz, some of which is coarsely crystalline. 



The crystalline schists also present many variations in structure 

 and composition, the most striking features being a tendency for 

 the segregation of the constituent minerals into fairly homogeneous 

 pockets or veins. Practically pure masses of actinolite, glauco- 

 phane, chlorite, talc, albite, and quartz may be obtained from the 

 same rock mass. Gradations between such occurrences and the 

 strictly schistose portions, composed of finely crystalline minerals 

 only, are to be found. Evidences of crumpling and distortion of 

 the mass after crystallization has taken place are revealed by 

 deformations (curvatures, twistings, partings, etc.) of the individua 

 crystals and by the curvature of the plane of schistosity itself. 



The true connection between the two formations is an obscure 

 one. Contact between the two was observed in a single instance, 

 and that of a rather indefinite character, the only feature worthy of 

 note being the tremolite which has been already described. The 

 chemical features seem to show that there is a general relationship 

 between the two formations, since both groups of rocks repre- 

 sent magmas, comparatively rich in magnesia and lime and poor 

 in iron and alumina. The rather unusual occurrence of soda in the 

 pyroxenite also indicates a relationship with glaucophane- and albite- 

 bearing schists, but there seems to be, as yet, no means of 

 determining the exact nature of this relationship. 



The occurrence of actinolite in the form of nodules many of 

 which are rounded and polished, though said to be not uncommon 

 in the Coast Ranges, is, on the whole, an unusual one, and suggests 

 an inquiry as to the geological peculiarities to which this feature is 

 due. Two possible theories (one chemical and the other dynamical) 

 suggest themselves. According to the former theory, the nodules 

 arose from peculiarities in the composition of the peridotites 

 and pyroxenites which preceded the serpentine, whereby from 

 certain centers of crystallization spherical aggregates were formed 

 and segregated as definite structures in the subsequent disintegra- 



