278 GEOLOGICAL SURVEY OF THE TERRITORIES. 
scopic examination, when the water commenced its work the material was in loose 
unconsolidated deposits. That it was thrown out as an ash, or rather deposited as 
a moya near its present location, is the most probable supposition. It seems, 
then, to have been taken up by the waves and. spread out as it is now found. The 
reason for this opinion is that the fragments are not worn as they would naturally be 
if they had been derived directly from solid rock by water action, and the decomposi- 
tion is not so gr°at as we should expect. The deposition appears to have been gentle 
but comparatively rapid, for there is no sign of violence or even of such decomposition 
as we should expect in slow deposition ; and showers of ashes falling on still water or 
a lake acting on an unconsolidated tufa bank answer best the conditions called for 
here. _ It is probable from the kaolinized feldspars and the macroscopic fragments of 
apparently older rocks that the latter are present in the tufa to some extent. This 
can best be explained by the supposition that it was deposited as a moya or mudflow 
within reach of the waters that have worked it over and deposited it in its present 
position. As we said before, the field evidence must be relied upon mainly in deciding 
such questions as these. 
M. EK. WADSWORTH. 
CAMBRIDGE, Mass., April 15, 1880. 
Another section, less carefully measured and noted with less detail 
than the other, was taken at or near the same place as Dr. Peale’s men- 
tioned at the beginning of this article, viz, at the extremity of one of 
the promontories jutting in a southwesterly direction into the middle of 
the upper chain of lakes, just west of the school-house* and about three 
kilometers west of Castello’s Ranch. The top of the hill was covered with 
granitic gravel and loose bowlders of dark scoriaceous trachyte; below 
this we found, passing, as before, from above downward, the following 
succession: 
Section in the northwestern lake. 
[By S. H. ScuppER and A. Lakes. ] 
Decimeters (estimated). 
1. Finely laminated yellow-drab shales; no fossils ......-......---.------------- 12 
2, Coarse decomposing yellowish shales; no fossils ...............-...----..----- 12 
3. Fine compact drab shales; perfect remains of plants and insects. Passing into. 15 
A, AAO XONS Sey GSS Wey INGOT Occ5 cosbes booube Cobo access Skoniedaeee dsee oeeken 6 
5. Heavily bedded, coarse-grained, crumbling sandstone, of a grayish yellow and 
whitish color, becoming ferruginous in places; partially lignitic -.---....-.. 60 
6. Chocolate and drab colored shales having a conchoidal fracture, passing below 
into whitish paper-like shales inclosed between coarse arenaceous laminae; 
PLAMbS Vamp SEC Sis Foe ee SERENE RN SN rT rete a UC ae 
Total thickness of shales above floor deposits. .....--.-- (Meters, estimated) 15 
These measurements being estimated are undoubtedly too great. The 
composition of this bluff is coarser in character than that of the section 
in the southern extension of the lake. The lignitic beds, which have 
been used for quarrying purposes, contain numerous fragments of reeds 
and roots not well preserved. The lower portions of the section corre- 
spond better with the other than do the upper beds, where it is difficult 
to trace any correspondence; No. 3 of the northwestern seems, however, 
to correspond to No. 16 of the southern series. The whitish paper shales 
lying at the base of this appear to be entirely absent from the southern 
section, and the distorted beds which crown the mesa are not apparent 
in the bluff, or, if present, are wholly regular. A more careful and de- 
tailed section of the bluff (for which we had not time), and particularly 
the tracing of the beds along the wall of the lake, would probably bring 
to light better correspondences. Directly in front of Judge Castello’s 
house, at a level of a little more than 2,400 meters, is a bed of fossil fish. 
Judging from the present physical condition of the basin, its age is 
marked as later than the movements which closed the cretaceous epoch 
and earlier than the last upheaval in the tertiary, which seems to have 
* Not the school-house before mentioned, which lies to the south of Castello’s Rauch. 
