Se wen 
625 
No. 2: Differs very little from the preceding, perhaps a little finer grained. 
No, 3: Much coarser than No. 2, made up of black and yellow angular frag- 
ments. Its matrix about the same as the body of No. 2. The black fragments, 
on being broken open, are seen to be dull in color, exceedingly fine grained, not 
glassy, but felsitic, also slightly vesicular. Occasionally an incipient sanidine 
crystal can be seen. . 
No. 4: Very coarse, but with practically the same composition as No. 3. Very 
loose and easily falling to pieces. Scoriaceous fragments more abundant. 
No, 5: Dirty yellow in color, more coherent; concretions of fine yellow silty 
material occasionally seen. It contains fossil teeth, probably of Bovide. 
No. 6: Practically the same as No. 3. 
No. 7: Concretionary structure very pronounced. These concretions are usually 
almost perfectly round and vary from only a few millimeters to 10 or 20 centi- 
meters in diameter. Concretions composed of the same material as the matrix. 
No. 8: Appears altogether to lack the conecretionary structure, at least this 
is so in the hand specimen; otherwise it differs in none of its essentials from 
No. 7. A slight efflorescence of a material which doubtless is sodium carbonate 
has appeared since the sample was received at the Bureau. 
This admirable series shows the difference in the conditions which 
prevailed, but at present we are unable to give any reliable data as to 
the rapidity of change. Considerations of this kind, together with 
questions as to the origin of the series, ete., will, it is contemplated, be 
taken up by another member of this Bureau in connection with his 
work on Taal Volcano, with which these deposits are closely related. 
This being the case, it is in this connection sufficient to state that 
the tuff-covered area as shown by Centeno on his map of the year 1885, 
extends beyond the limits given by the latter to the Loboo Mountain 
area and even to the eastern slopes of the range. 
This deposit, or series of deposits, is in some places very recent, as is 
shown by the fossil] rice blades, identical with those growing in the 
fields to-day, which occur in it, so that at least one mighty cataclysm 
probably took place within the historic period and at a time when this 
country had partly risen from the sea. 
Reference to Plate I will suggest something of the field relations of 
the tuff obtaining in this region, 
ECONOMIC GEOLOGY. 
Jonsidering the stage of the prospecting which is being carried on in 
this district, it might be premature to speak of the mineral veins as 
ore deposits. The country might be fairly well mineralized, without 
the occurrence of any workable body of ore. 
For the most part, the metallic minerals are confined to veins of the 
fissure type, but some indications of lateral secretion in the country 
rock itself are present. Two sets of yeins appear to be more prominent 
than the rest, the main one of Fo strikes in the direction of N. 70° W. 
whereas the other trends N. 45° to 57° W. By comparing the former 
direction with the general trend i the Loboo Range (see map, Pl. I1) 
it is seen that the two agree very closely. 
