33 * 
1877O Southern Hemisphere , 
He describes Terra del Fuego as largely covered with till 
and boulder clay perfectly unstratified, and in which he 
looked in vain for marine remains. 
On the western coast the ice from the Chilian Cordillera 
appears to have flowed across the Straits to the island of 
Chiloe, as Darwin found it covered with large boulders of 
granite and syenite that had come from the mainland. On 
one of the Chonos Islands he found a quantity of commi- 
nuted marine shells in the drift, and in Chiloe two or three 
fragments of a Cytherea .* We may compare these fadts 
with those in the northern hemisphere, where the drift in 
the southern shores of the Baltic, brought by land ice from 
Scandinavia, is found — as in the vicinity of Bromberg — -to 
contain broken and worn sea-shells that have probably been 
picked up in the passage of the ice across the ocean-bed. 
Bearing just the same relation to the Glacial period in 
South America as the loess of the Rhine and the Danube 
does in Europe, and still more resembling the diluvial clay 
of the South of Russia, the Pampean mud is spread out in 
Rio Plata, Banda Oriental, and Entre Rios. It covers an 
immense tradt of country. Darwin passed continuously 
over it from the Rio Colorado to St. Fe Bajada, a distance 
of 500 geographical miles, whilst M. d’Orbigny traced it for 
250 miles farther north. From east to west, in the latitude 
of the Plata, it extends for at least 300 miles. 
It is a reddish, slightly indurated, argillaceous earth, 
sometimes more than 100 feet thick, with lines of calcareous 
concretions, and occasionally changing into a compact 
marly rock. Marine shells are found scattered over the 
surface of this deposit at some places ; but Darwin notices, 
as a remarkable fadt, their absence throughout the deposit, 
excepting in the uppermost layers near Buenos Ayres. 
Even microscopical organisms appear to be very rare, and 
only found in the lower part of the deposit. Thus, in some 
of the red mud scraped from the tooth of a Mastodon found 
at the bottom of the Pampean mud at Gorodona, Prof. 
Ehrenberg found seven species of Polygastrica and thirteen 
species of Phytolitharia. Of these nearly all are of fresh- 
water origin, only three being marine. At Monte Hermoso, 
in Bahia Blanca, the lower part of the Pampean mud con- 
tains a similar assemblage of microscopical organisms. 
Prof. Ehrenberg considers that they must have lived in 
brackish water. 
The most remarkable fa efts respecting the Pampean 
* Trans, Geol. Soc., vol. vi., p. 426. 
