34 BULLETIN: MUSEUM OF COMPARATIVE ZOOLOGY. 
point, which is the more worthy of investigation, because it may throw 
some light on an opinion often promulgated of late years, that there 
is a tendency in the Chilian coast, after each upheaval, to sink grad- 
ually and return towards its former position.” (Lyell, Principles of 
geology, 11th ed., New York, 1887, 2, p. 156). I found this view 
still current at Talcahuano, and it is evident from the view referred 
to that no marked permanent change of level has affected the ancient 
ruin on the beach at Penco since it was constructed. 
The railway from Concepcion to Penco traverses an outcrop of 
coarse, waterworn conglomerates at Paradero de Santa Ana, evidently 
a member of the Tertiary series which underlie the plain between the 
Coastal Cordillera and the ridge of crystalline rocks which form the 
Tumbres Peninsula on the seaward side of the Bay of Concepcion. 
In the bank of the bay shore immediately south of Penco, coarse 
gravels composed of pebbles of crystalline rocks and occasionally 
large rounded stones crop out in the railway cut in marked uncon- 
formity upon sandstones. The change from the blue color of the 
gravels at the base to orange at the top of the bluff is evidently an 
effect of weathering now in progress. Certain portions of the pebble 
beds contain stones a foot or more in diameter. The deposit is 
mainly stratified with flattish ovoid pebbles lying in the planes of 
bedding. In the lower part of the exposure the paste of fine material 
is less obvious than in the upper portion. Lenticular beds of sand 
and finer gravel appear at intervals in the section, pointing to inter- 
mittent or shifting currents or streams. From its general relations 
and want of consolidation I supposed the deposit to be of Pleistocene 
date and possibly not older than the bench which at about the same 
elevation can be traced around the seaward face of the Tumbres 
district at the Paps of Bio Bio. If this correlation be correct the 
deposit may bé of marine origin, but no fossils were seen in any part 
of the section. 
On the exposed face of the gravel bluff loose materials were sliding 
down in such a manner as to afford an instructive example of the 
post-depositional striation of pebbles. A large rounded cobble 
protruding from the section (Fig. 6) was well striated on its exposed 
surface by pebbles sliding down over it in the wasting of the upper 
part of the bluff. I observed this process in action, and it showed the 
necessity of taking every precaution in accepting detached striated 
pebbles as evidence of glaciation. 
On December 18 I left Concepcion for Valdivia to examine the shore- 
lines of that district for the reason that Darwin stated that here he 
