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 be 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 181 left Concepcion for Valdivia to examine the shore- 

 lines of that district for the reason that Darwin stated that here he 



