214 The American Geologist. April, 1891 
slates which have been pushed aside by them, offers an insuper- 
able barrier to this theory, as does also the almost universal 
presence of traces of crystalline structure and the frequent occur- 
rence of amygdules. 
Pikes and bosses of granite occur at intervals along the lode 
near Jacksonville, Tuolumne count}-, the fissure has broken through 
a knot of granite one thousand feet across. 
Many dikes of talc schist and other less altered ones, which still 
show crystalline structure, are to be seen along the lode, especially 
through the northern part of Mariposa county. 
In Calaveras count}', a short distance from the lode, there is a 
hill of knotty talc schist, in which are imbedded small nodular 
masses of dark, coarsely crystalline rock, composed of calcite, 
magnetite and a little pyrite. The talc is rendered knotty by 
aggregations of granular calcite crystals and shows all gradations 
between an almost massive form in which the arrangement of the 
calcite pseudomorphs as well as the structure indicate a once 
crystalline condition, and a very fissile schist in which the calcite 
crystals have almost disappeared and the talc fibres have only a 
slightly wavy appearance. The massive portions undoubtedly 
represent the original structure which, through some inherent 
difference of certain parts, was preserved, as were the nodules ob- 
served so often in the serpentine. Whatever was the composition 
of this rock, in the process of substitution which has gone on, 
everything has been replaced by calcite, except the iron. The 
pyrites owes its origin to percolating solutions, while the small 
quartz veins which are scattered through the rock ma}- be due to 
that also or, what is more probable, to the segregation of a part of 
the silica of the original mass. 
As an example of the complexity of the country rock and of the 
magnitude which the Mother Lode sometimes assumes, Quartz 
mountain, Tuolumne county, will best serve. "The Mountain" is 
about six hundred feet wide, nearly half a mile long, and two 
hundred and fifty feet high. It is formed wholly of quartz and 
vein matter, the latter consisting of mariposite and dolomitic mate- 
rial. In the middle and forming the summit is a great body of 
massive quartz. On the west side another nearly as large, and on 
the east a smaller one. The vein matter between them is filled 
with a network of small quartz stringers. 
Beginning in the east and going west for a mile, the following 
