54 



University of California. 



[Vol. 2.. 



seem possible that a rigid body could be penetrated as the gabbro 

 has been and yet retain its solid condition. At the spot where the 

 photograph was taken, it seems as if the gabbro must have been the 

 more fluid of the two, but in other places a short distance away 

 the reverse is certainly the case. Although in general the contact 

 is sharp, there is sometimes a slight blending with long narrow arms 

 of the gabbro projecting into the serpentine. One important fact, 

 which would lead to the supposition that the phenomenon is due 

 to an invasion of the gabbro by the picrite is, that almost 

 everywhere near the contact, the latter contains more or less feld- 

 spar in aggregates which present to the eye a slight resemblance to 

 poikilitic crystals, often drawn out in rude parallelism. An inclu- 

 sion of a boulder-like mass of gabbro in the serpentine was noted 

 which has a peculiar character. It is about two feet in diameter, 

 and shows concentric bands of feldspar arranged on three sides 

 near the periphery. The simplest explanation of the inclusions in 

 the serpentine, and probably the true one, is that of absorption of 

 the gabbro by the more magnesian magma. The latter must have 

 retained its heat for some time, and literally eaten into the gabbro, 

 the irregular contact being due to fissures along which resorption 

 would proceed faster. 



A body of gabbro and related rocks lying south of the west- 

 ern end of the serpentine, and forming one of the projecting points, 

 offers a most interesting field for the study of many different 

 intrusions of varying character. A part of it consists of gneissoid 

 and finely banded troctolite. In other portions there is a confused 

 mixture of gabbro of different kinds. Patches of a banded gabbro 

 appear inclosed in a somewhat similar rock, whose banding makes 

 an angle with that of the inclusion, the boundaries not being strongly 

 marked, as if a partial fusion of the latter had taken place. Across 

 one end of the area, a dark, fine-grained norite-gabbro has been 

 intruded obliquely to the banding of the larger mass, while along 

 the contact there is a differentiated layer of almost pure feldspar. 

 Dikes are seen which vary in different portions, as well as those 

 which are uniform and distinct. Among the coarsely crystalline 

 rocks the troctolite is prominent. The darker, finer-grained dikes,, 

 including gabbros, norite-gabbros with or without olivine, and 



