GEOLOGY OF PERU—ADAMS. 407 
of marine sponges are actually present in the deposits. Although 
Duefias finally accepts the lacustrine theory for the deposits, he goes 
rather far when he remarks that it is nothing wonderful to suppose 
that Lake Titicaca once extended into the Department of Cuzco. 
From what the writer has seen of the topography it appears alto- 
gether improbable; and, moreover, the theory of local lakes would 
account in a more satisfactory manner for the occurrence of the for- 
mations. 
Tertiary of the Amazon region. 
James Orton, in his explorations of the upper Amazon Valley, 
collected some shells from Pebas, which he submitted to Gabb, who 
determined them (1868) as late Tertiary. Because of the finding of 
these shells, Orton refuted the theory of the glacial origin of the 
clays of the Amazon basin presented by Agassiz and discussed later 
in this report. Orton (1870) gives a description of the exposures 
along his route of travel. He says that along the Napo River the 
only spot where the rocks are exposed is near Napo village, where 
there is a bed of dark slate dipping east. Farther west, at the foot 
of the Ecuadorian Andes, the prevailing rock was found by him to 
be mica schist. The entire Napo country is covered with an alluvial 
bed on an average 10 feet thick. The formation of the bluff near 
Pebas he described as consisting of fine laminated clays of many 
colors, resting on a bed of lignite or bituminous shale and a coarse 
iron-cemented conglomerate. 
After Gabb described the collection of shells from Pebas, a larger 
collection was made by Mr. Hauxwell, a part from Pebas but most of 
- them from 30 miles below Pebas, at Ekchinn, Among them Conrad 
found (1870) seven species of Pachydon (Gabb),a genus which does 
not have any living representative and is very different from any 
existing fresh-water genus. He says that it is not possible to state 
without doubt what the relative stratigraphic position of the group 
may be, but if all the species are extinct it can not be later than Ter- 
tiary, and that it may have lived in fresh or brackish water, but it is 
certainly not of marine origin. 
A collection made by Mr. Steere at Pebas was examined by Conrad 
(1874), who questioned there being evidence of the marine origin of 
the shells. 
QUATERNARY. 
Pleistocene glaciation. 
OCCURRENCE OF SNOW PEAKS. 
Humboldt, in his personal narrative (1814), called attention to the 
absence of snow peaks between the Nevada Huaylillas in latitude 
(° 55’ and Chimborazo in Ecuador. 
88292—sm 1908——27 
