244 



University of California. 



[Vol. 2. 



About five miles north of the port of Montijo, this red shale 

 has been baked by the intrusion of an eruptive not exposed, into a 

 bright red mica schist as ancient in appearance as Archaean schists 

 in the United States, and sufficiently extensive to have a consider- 

 able road cutting entirely in it. This is one of the finest cases of 

 contact metamorphism of comparatively recent date known to me. 



The Panama Formation. — In the country southwest of Santiago 

 there is above the red shale a harder, more massive formation, 

 usually of lighter color. It varies from white through gray to a 

 dull purplish tint. Never is it laminated but sometimes it is seen 

 to be heavy-bedded. Macroscopically it appears to be composed 

 of a fine granular material. I consider it largely a water-deposited 

 fine volcanic ash or rhyolitic tuff. In places it is coarse-grained 

 and even slightly conglomeratic, in which cases it is well indurated. 

 Where not eroded the thickness is probably at least several hun- 

 dred feet. 



East of Santiago there is, above the red clay, a great series of 

 usually soft and chalky, non-laminated but water-deposited, fine- 

 grained, clay-like materials (rhyolitic and trachytic tuffs) of a color 

 prevailingly white to gray and rarely red or brown. This white, 

 chalky deposit has been penetrated at the Remanse mine to a depth 

 of over 600 feet, but contains layers which weather out like lava. 

 East of the Santa Maria River the formation is widely developed, 

 although many of the small hills which stand on the plain appear 

 to be composed of trap rocks such as diorite, porphyry, basalt, etc. 



The series of soft formations over the Santiago shale, consisting 

 of the purple basal conglomerate, the red shale, and the white and 

 light gray semi-massive tufaceous formation, are conformable to 

 each other, were laid down in immediately succeeding epochs in 

 the same body of water and belong to the same period of geologic 

 time. This was separated from the epoch of deposition of the 

 much harder and older-appearing Santiago formation by a consid- 

 erable erosion interval, during which was formed the broad shallow 

 basins in which the Tertiary strata are now found. 



In its rhyolitic composition, prevailing white color and chalky 

 texture (but not its heavy bedding) the Panama formation more 

 nearly resembles the lower 1,000 feet or volcanic division of the 



