WOODWORTH: GEOLOGICAL EXPEDITION TO BRAZIL AND CHILE. 131 
Malvoa Station, 79 kms., alt. 43 M. (141.0 ft.). Good terrace on 
opposite or southwest side of river. At railway station there are clays. 
San Rosendo Station, 85 kms. alt. 46 M. (154.8 ft.). East of the 
Station there was in 1908 an excellent exposure of gravels and sands 
in a deep cut, rising about sixty-five feet above the railway, or to an 
elevation of 220 feet above sea-level. The annexed 
section is from a drawing made on the spot. 
(Fig. 37). 
This section reveals a succession of river deposits 
varying from sands like those now transported in 
this portion of its course by the Rio Bio Bio to 
coarse gravels including large boulders such as 
demand ice-rafts or the proximity upstream of 
glacial conditions. 
The lowest bed exposed (see Fig. 37) consists 
of dark sand with pebbles of a voleanic rock. 
Above this comes a coarse gravel including a 
boulder of gneiss about seven feet long. Next 
in the section is sand with thin bands of volcanic 
pebbles. Above these layers comes about twenty- 
five feet of dark sands with a thin band of volcanic 
pebbles. Surmounting this and forming the sur- 
face is a layer, about twenty-feet thick, of coarsely 
bedded gravels and boulders, the cross-bedding of  py6. 37. — section of 
which suggests the structure of a delta front. Pleistocene terrace 
There are in this section thus the records of two is Brae ance 
episodes when the river transported to this point 
coarse gravels and boulders which it is to be presumed indicate con- 
temporary advances of the local glaciers or times of unusual melting 
and discharge of coarse débris. 
I saw no marine shells in any part of this terrace or on its surface, 
and no evidence of the presence of the sea in the deposition of the 
materials. The structure is quite like that of many glacial river 
deposits in the inland portions of glaciated North America. The 
lower bed of coarse gravel with boulders must have been deposited 
at or above sea-level as is also the case with the uppermost bed of like 
materials. The aggradation of the valley under glacial stream-action 
affords a simple explanation of these deposits without recourse to the 
hypothesis of a change of level in relation to the sea. 
This section is the most reliable in its bearing on the altitude of the 
terraces, since those lower down the river were estimated only from 
