416 ANNUAL REPORT SMITHSONIAN INSTITUTION, 1908. 
some of the white chalk material and some beds of impure concre- 
tionary limestones similar to what occurred at the type locality near 
Pisco. The so-called chalk material was analyzed by the Corps of 
Engineers of Mines and found to consist principally of silica, with 
small amounts of lime and alumina. A microscopic examination 
showed it to contain many diatoms and what appeared to be vol- 
canic ash. 
In traveling by steamer from Pisco to Lomas the Pisco formation 
can be seen forming the sea cliffs and rising to the table land of Ica. 
Although some fossils have been found, they have not been studied 
critically. The age of the Pisco formation is not surely known. The 
writer has assigned it to the Pliocene provisionally, since it is over- 
lain by deposits which are probably of Pleistocene age, and there is 
no information which shows the necessity of assigning it to an 
earlier time. 
TERTIARY OF THE SOUTHERN COASTAL PLAINS. 
The Moquegua formation. 
The writer has given this name to the formation which occupies 
the southern coastal plains. It has been described locally, by Forbes 
and others, as already mentioned in this paper, but no one had 
journeyed sufficiently over the plains to learn that it was coextensive 
with them. The strata which constitute it can be studied conven- 
iently in the valley of the Moquegua River, especially near the town 
of the same name. It is also well exposed in the valleys of all the 
streams which cross the plains, since they have cut deep canyons. 
The eastern limit of the formation is at the foothills of the Andes, 
and the western limit is formed by the chain of coast hills. It 
reaches to the Pacific Ocean in the interval between the coast hills 
of Peru and the Morro of Arica, which is the northern extremity of 
the coast hills of Chile. The character of the rocks which constitute 
the Moquegua formation has been well outlined by Forbes. They 
consist of sands with some clays, a large quantity of detrital material 
derived from igneous rocks, but especially noticeable are the thick 
beds of voleanic material which appear to have been deposited in 
water and interbedded with sands. In the valley of the River Vitor, 
which descends from the Andes past the volcano Misti which is 
located near Ariquipa, beds of lava may be seen which have de- 
scended from the voleano and extended over the plains, where they 
form a capping on the Moquegua formation. The age of the voleanic 
rocks is not certainly known, and there has been no opportunity to 
determine the age of the Moquegua formation, since no fossils have 
been found. It is generally stated that the volcanoes of southern 
