Notice of Syenitic Rocks from California. — Turner. 383 
tered iron sulphurets ( FeSa ) in minute specks. The brown 
color is due to abundantly disseminated limonite. The micro- 
scope shows the dike rocks, where not replaced by silica and 
dolomite, to be composed almost entirely of interlocking 
grains of feldspar with some larger twinned feldspars, in fact 
identical as to composition with other similar dikes, which 
may be seen along the Mother lode one mile to the northwest 
or about one mile due east of Jacksonville, and to the east of 
Moccasin creek on the south side of the river. Although the 
dike to the east of Moccasin creek contains at several points 
numerous quartz veinlets, at no point was there as good evi- 
dence obtained of the formation of quartz veins of some size 
by replacement of the feldspar of the dikes with quartz and 
dolomite, as at the place just described, on the north bank of 
the Tuolumne river. 
In the bed of Moccasin creek, at its mouth, is a large crop- 
ping of white granitoid rock. This is the north end of the 
Moccasin creek dike, which extends thence nearly or quite 
continuously southeasterly for about two and a half miles. It 
crosses the road to Groveland, about one-third of a mile east 
of the bridge over Moccasin creek. Except at the north end, 
it lies entirely to the east of the creek, gradually increasing 
in altitude and in distance from the creek to the southeast. 
This dike was first noted by the writer in 1886, but no investi- 
gation was made as to its nature. It is mentioned by H. W. 
Fairbanks in a paper on the Mother lode,* but was called by 
him a granite dike, which rock indeed it resembles to the 
naked eye, and as noted above the north end of the dike is a 
soda-granite as the term is used by Rosenbuseh, or soda- 
granulite, according to Michel Levy. Specimens of tins dike 
were collected at a number of point-. The granitoid portion 
at the north end contains a good deal of quartz, and may be 
called a soda-granulite It is composed of -quartz, muscovite 
and albite or soda-feldspar. Analysis of this soda-granulite 
is given in the table (No. I'fl'.l S. X). By far the larger part 
of the dike, however, is made up of albite feldspar only, and 
is mostly finer grained than tin- granitoid rock of the north 
end. It may be designated a soda- syenite (albitite) porphyry. 
Thin sections from different portions of the dike show a 
*10th Ann. Rep. State Min. California, p. 45. 
