March 14, 1902.J 



SCIENCE. 



411 



An Instance of Variability in a Rock 

 Magma: IT. W. Turner, San Francisco, 

 Cal. 



The instance referred to is the granolite 

 area east of Sonora in Tuolumne County, 

 California. This area is enclosed on three 

 sides by the sedimentary rocks of the Cala- 

 veras formation, and on the east by a 

 granite and gneiss series of older age, so 

 that it is practically an enclosed area. The 

 rock is designated, on the Sonora geological 

 map of the United States Geological Sur- 

 vey, granodiorite, but it is not a typical 

 example of that rock. It contains at most 

 points some orthorhombic pyroxene. The 

 rock varies from a granodiorite contain- 

 ing nearly 63 per cent, of silica to olivine 

 gabbro containing about 43 per cent, of 

 silica, there being all gradations between 

 these extremes. The mass is intrusive in 

 the Calaveras formation. The gabbro 

 forms a hill in the interior of the area. 

 The variation in mineral and chemical com- 

 position is not regarded as being due to 

 absorption of material from the surround- 

 ing rocks, but to a differentiation during 

 crystallization. On the west and south the 

 Calaveras rocks contain much limestone, 

 but the most basic facies of the rock, the 

 olivine gabbro, is not near their contact. 

 Moreover the limestone is not a magnesian 

 limestone, and if we seek to explain the 

 high lime content of the gabbro (14.27 per 

 cent.) by an absorption of lime from the 

 adjoining calcareous rocks, we are also 

 brought to account for the high magnesia 

 content (7.65 per cent.) of the gabbro from 

 a similar source, and there are no magne- 

 sian rocks in the neighborhood outside of 

 the granodiorite-gabbro mass, except small 

 amounts of perknite or amphibole-pyroxene 

 rock, and these are not, except at one point, 

 in juxtaposition to the granodiorite-gabbro 

 area. There perknites may indeed be 

 themselves the extreme result of differen- 

 tiation of the granodiorite. There are 



abundant dikes of diorite in the grano- 

 diorite, and pegmatite and quartz-tourma- 

 line dikes or veins. 



Triassi'c Reptilia from Northern Cali- 

 fornia: John C. Merriam, Berkeley, 

 Cal. 



Reptilian remains were first discovered 

 in northern California in 1893, when Pro- 

 fessor James Perrin Smith obtained two 

 short series of vertebrfe and two arch bones 

 in the Triassic limestones. These speci- 

 mens were described by the writer in 

 1895, under the name of Shastasaurus, and 

 were thought to belong to a form closely 

 related to the Ichthyosauria, though they 

 did not appear to find a place in any known 

 genus. During the summer season of 

 1901 a quantity of new material was ob- 

 tained from the original locality. The col- 

 lection inchides considerable parts of five 

 skeletons, also numerous loose limb-bones, 

 vertebrae, ribs, etc. Nearly all of the 

 specimens belong to the genus Shastasaurus, 

 of which there are several well-character- 

 ized species. Two nearly complete series 

 of dorsal and cervical vertebrae show 

 Shastasaurus to be characterized by possess- 

 ing single-headed ribs on all of the verte- 

 bra in this region excepting the anterior 

 8-9. In the cervieals the parapophysis 

 is relatively small and in the anterior 

 dorsal region it disappears entirely. As 

 far back as the middle dorsals the articu- 

 lar surface of the diapophysis is confluent 

 with that for the reception of the upper 

 arches. The anterior and posterior limbs 

 have not been found together, but are 

 known from species having the same type 

 of vertebrae and ribs. The anterior limb 

 is ichthyosaurian in type, but the trans- 

 verse diameter of the humerus is much 

 greater than the longitudinal. The radius 

 and ulna are very short and are separated 

 by a considerable space. In the posterior 

 limb the femur resembles that of Ichthyo- 



