50 The American Geologist. jan. isoo. 
Its general outline is in the form of a parallelogram, its great- 
est length about 18 miles, and greatest width about 12 miles, 
with a shore line of nearly 45 miles. 
On the northeastern side of the island and midway between 
the north and west points a reef extends out to a distance of 
one and a quarter miles. 
The channels between this island and Santa Cruz on the 
east, and San Miguel on the west are respectively six miles 
and four miles in width. 
The outline of the island is bold and no harbors exist 
around its shore, but there are several good landing places, 
and a wharf has been built about the centre of Five -mile 
bight, where vessels can load and unload in safety. 
This island had been described as composed of sandstone, 
but the first thing noticeable on landing at the west end of the 
island was the volcanic character of the rocks. 
At the wharf we found a good exposure of strata forming 
cliffs about 30 feet in bight, the lower portion, for 15 feet above 
the sand of the beach, composed of stratified sandstone, fine 
grained and destitute of fossils, with an occasional stratum of 
breccia or conglomerate. These strata have a dip of about 12 
degrees southeast. The upper portion of the cliffs consists of 
a horizontal deposit of fragments of rhyolite, trachyte, vesicu- 
lar basalt, and white bituminuos shale. The fragments grad- 
ually decrease in size from the bottom where they are cement- 
ed together by volcanic sand ; this is covered by deep and ap- 
parently good soil. 
In some places the rock fragments of the upper half of the 
cliffs have been water-worn and form conglomerate. 
This character of rock extends from the wharf southeasterly 
to near the sand point at the southeastern extremity of the 
island, where it culminates in a hill of volcanic rock 175 feet 
high, which is exposed for some distance in a southeasterly 
direction from the beach on the north side of the point. 
The rocks have a marked tendency to weather into fantas- 
tic forms, the angular rocks becoming rounded by disintegra- 
tion, with irregular cavities and caves worn by the winds 
which have been used as dwellings by the aborigines as is indi- 
cated by fragments of shells and other debris in large quan- 
tities. 
At the northeastern extremity of the island is found a coarse 
