422 J. P. Kimball—Geological Relations and Genesis 
spathic aggregate under conditions of extreme exposure to- 
weathering action, all parts of the dioryte must be assumed to 
represent its effect, however unequal, and insusceptible of meas- 
urement without the partial preservation of the original type 
for comparison. This consideration is one of importance in 
the present case, because a large source of ferric oxide must be 
looked for to account for its accumulation, under favorable 
circumstances of drainage, in the form of the iron-ore bosses- 
along the lower edge of the dioryte mantle, at its contact with 
the underlying syenyte. 
Two series of cireumstances have determined the loci of 
D 
the intermittent action of percolating acidulated waters and of 
alkaline bicarbonates. 
1. Proof of the coralline parentage of the iron-ore bosses 
is the preservation in nearly all of them of fossil corals, or 
at least of casts of coral. Such casts are found toward the 
tion parts. These are in general siliceous from the segregation 
of silicates. While the lime carbonate of the casts referred to- 
is replaced by ferric oxide, the cells of the corallum are filled. 
out with segregated matter, more or less chloritic from secon- 
dary alteration. 
arger bosses, corresponding to coralline masses, exhibit 
a concentric structure characteristic of segregation by foliation 
or external deposition. The smaller ones, on the other hand, 
frequently present the peculiar warped surfaces characteristic 
of the coral rocks, and such as may be seen on every cliff or 
detached mass of coral rock in the terraces along the present 
coast. 
The larger bosses may in a general way be described as len- 
ticular bodies, any section of which is approximately elliptical. 
The smaller ore-bodies are of irregular shape and suggest a 
fragmentary relation to the larger ones, especially as they are 
always found near the larger, and invariably in such relations 
as would correspond to the superior surfaces of corallines 
referred to their original relations with their syenyte base. 
he position of all the ore-bodies is on the inner or upper 
parallel to the crest of the Sierra as wel] as to the present coast, 
tends to show the parent corallines to have been involved im 
