GEOLOGY OF PERU—ADAMS. 
Peru began their activity in Ter- 
tiary times and some of them are 
still active, although no great 
lava flows have come from them 
in recent times. The writer 
has provisionally assigned the 
Pliocene age to the Moquegua 
formation, thus making it con- 
temporaneous with the Pisco 
formation to the north. There 
appears to be no reason for con- 
sidering it as of greater age, and 
in outlining the history of the 
coast the Pliocene age seems for 
the present satisfactory. 
The thickness of the Moquegua 
formation is variable, since it was 
apparently deposited in a trough 
between the coast hills and the 
foothills of the Andes (see fig. 
8). From measurements made in 
some of the canyons a thickness 
of 1,500 feet may be assigned. 
QUATERNARY DEPOSITS. 
Pleistocene. 
THE PACASMAYO FORMATION, 
At Pacasmayo, in the southern 
part of the northern coastal 
plains, the sea cliff consists of 
stratified conglomerates mixed 
with sand and occasional clay 
beds (see pl.3). The formation is 
also well exposed at the mouth of 
the Jequetepeque and along that 
stream inland. At Eten the sea 
cliff consists of a homogeneous 
sandy clay. To the north of Eten 
for a considerable distance the 
coast is low near the shore and 
there are no good exposures, so 
that the writer has not been able 
to trace the Pacasmayo formation 
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