THE GEOLOGY OF THE CHINCHAS ISLANDS. 
175 
The Society met on the 14th May, 1856, on which occasion the 
following Paper was read. 
ON THE GEOLOGY OF THE CHINCHAS ISLANDS, PERU, SOUTH AMERICA. 
BY JOHN ROBERT KIN AH AN, M. B. T. C. D. 
The district about to be described consists of three islands situated 
in the South Pacific Ocean, about twelve miles from Pisco, on the 
coast of Peru, in lat. 13° 44' S.; long. 76° 13' W. 
Though small in size, the largest island probably not being more 
than three miles round, they are and have been for some time the 
seat of a busy commerce, as they abound in guano; and it was whilst 
taking in a cargo of this commodity that opportunity was afforded 
me for obtaining the materials for these notes. The islands are three 
in number, and surrounded by several large detached rocks. They 
go by the names of North, Middle, and South Islands. 
In their physical characters there is a strong resemblance between 
them; high precipitous cliffs for three-fourths of their circumference; 
the rest of their coast line, low cliffs and a few sandy coves,—these 
latter having more or less complete reefs of rocks crossing their en¬ 
trance—the beach, wherever it does exist, being a coarse shingle. 
The cliffs in the North and Middle Islands are highest at the 
north-west end of the islands, where it gradually slopes away south¬ 
ward and eastward ; the coves already mentioned generally being 
to the eastward. 
In the Middle Island the rock appears to rise gradually from the 
north, and finally culminates the guano as a conspicuous white rock. 
The surface of the North Island, as far as can be seen, is slightly 
depressed in the centre, having the level broken by rounded pro¬ 
minences. 
Narrow channels separate the islands, and are of from a quarter 
to nearly a mile in width, their depth varying from 2-J to 30 fathoms, 
the bottom either rock, sand and shells, or gravel. That between 
the North and South Islands is becoming altered in its characters 
every day, owing to the enormous quantity of ballast thrown over¬ 
board there; but the channel between the Middle and South Islands 
remains yet unchanged. Owing to the direction of these two islands, 
it is much narrower and more sheltered than the other ; in conse¬ 
quence, the shores on this side of the Middle Island are nearly all 
