PERMO-CARBONIFEROUS GLACIAL DEPOSITS 319 
of hills was reached, where quartzite, mica schist, and slate were 
encountered. 
Sections were examined a few kilometers up the river from the 
station and several fresh-looking outcrops of tillite were found at 
the water’s edge. Ascending the slopes from such outcrops one 
finds weathered tillite for a few hundred yards, then a cliff of tillite, 
followed by a covered belt where only quartzite pebbles can be 
seen for a height of about 15 or 20 meters. A second cliff of tillite 
reaches 85 meters above the river and is followed by quartzite to 
the top of the ridge. The lower bed of quartzite seems to be inter- 
glacial, corresponding to the band of quartzite and water-formed 
conglomerate seen in the railway cuttings. 
A section a kilometer or two down the Sauce Grande shows no 
base to the tillite, which has a thickness of 90 meters, as determined 
by aneroid, and is covered by quartzite including a band of tillite. 
None of the sections was entirely satisfactory, since on the gentler 
slopes the sclid rock is more or less hidden; but the thickness of the 
glacial beds seems to be not less than 60 meters and may be much 
more than that. 
An excellent account of the glacial deposits of Sierra- de la 
Ventana is given by Keidel in La Geologia de las Sierras de la 
Provincia de Buenos Ayres (1916), as mentioned in the introduction 
to this paper; and the statement is made that the origin of a 
number of the inclosed bowlders is unknown. Keidel puts stress 
on the resemblance of these deposits to the Dwyka, but gives no 
proofs of their age except that they are later than the Devonian, as 
shown by the inclusion of pebbles of limestone with Devonian 
fossils. The hard and somewhat metamorphosed character of the 
rock, which seems to suggest a greater age, is to be accounted for 
by the action of orogenic forces. One of Keidel’s plates represents 
the tillite as somewhat folded in a way that would add to the 
apparent thickness of the bed, but in my own field work no clear 
evidence of folding was seen, though compressive action was evident. 
TILLITE NEAR SAN JUAN IN WESTERN ARGENTINA 
Following a plan suggested by Dr. Keidel an excursion was made 
to exposures of tillite in western Argentina somewhat south of 
