ROCKS FROM HONDURAS, CENTRAL AMERICA 529 
odiorites. Near the town a rounded hill is composed of felsodacite 
intruded by diorite. The diorite is a medium- to coarse-grained 
type consisting of hornblende and oligoclase. The hornblende is 
pleochroic, chestnut brown to light yellow. The oligoclase is 
occasionally replaced along the albite twinning planes by magnetite. 
Tonalite porphyries containing phenocrysts of quartz and oligoclase 
in a glassy groundmass are frequently exposed, as are also agglom- 
erates containing pebbles of the porphyries. 
A biotitic tonalite collected 8 miles up the Congrejal valley at 
an elevation of about 300 feet is pure white in color and coarsely 
crystalline. It consists of predominating oligoclase feldspar and 
quartz with occasional flakes and bunches of biotite a centimeter 
in diameter. A granodiorite which consists of oligoclase-albite, 
microcline, quartz, and hornblende was collected near the same lo- 
cality. The rock has been subjected to great strain and the 
cracks are filled by a mass of small quartz crystals. The tonalite 
is seen in the field to be cut by the granodiorite, but the contact 
shows very little chilling of the latter rock. A dark-greenish 
porphyry cutting the granodiorite and a breccia composed of frag- 
ments of granodiorite in a granular matrix, but of uncertain relation- 
ship_to the other rocks, are seen south of large exposures of the 
granodiorite in the river bed. North of these exposures, about 5 
miles up the valley, quartz veins are very abundant, cutting a 
rock which looks like a hydromica schist, but which is probably a 
metamorphosed igneous rock. 
Near the mouth of the Masica valley, 25 miles southeast of 
La Ceiba, there are found tonalites and allied rocks similar to those 
exposed in the Congrejal valley, but here associated with basic 
types. An olivine diabase was collected which is composed of 
labradorite, augite, olivine, biotite, a little brown hornblende, and 
pyrite. A coarse-grained black wehrlite was also found consisting 
of olivine and augite in about equal proportions and a very small 
amount of labradorite. The olivine crystals often include rounded 
and resorbed bits of augite. 
At San Francisco, 15 miles southeast of La Ceiba, basalt 
porphyry bowlders with labradorite phenocrysts 2 to 3 cm. in 
