METAMORPHISM BY COMBUSTION OF THE HYDRO- 
CARBONS IN THE OIL-BEARING SHALE OF 
CALIFORNIA? 
RALPH ARNOLD AND ROBERT ANDERSON 
Washington, D. C. 
CONTENTS 
Introduction. 
Instances in Which the Shale Is at Present Burning. 
Typical Occurrences of Burnt Shale. 
Depth to Which Alteration Has Extended. 
Lithologic Character. 
Cause of the Alteration. 
Range in Time of the Phenomenon. 
INTRODUCTION 
A unique variety of metamorphism has been at work locally in 
many regions of bituminous rocks in California, where a process of 
combustion of the hydrocarbon contents has altered the naturally 
white, soft shale to a rock of brilliant rose or brick-red color, and 
rendered it in cases hard and vesicular like scoriaceous lava. The 
resemblance of the products to those of volcanoes and the existence 
of centers like solfataras where the process of burning has been going 
on during the last half-century, has given rise to the statement that 
there were living volcanic vents in Santa Barbara County. Though 
the combustion is usually local in its effects, the number and wide dis- 
tribution of the occurrences of burnt shale lend importance to the 
phenomenon. The presence of burnt shale at depths varying from 
go to 1,040 feet below the surface, as discovered in the drilling of oil 
wells, proves that the burning has taken place deep down within the 
oil-bearing formation, as well.as at the surface where it has been 
more commonly found. And further, the discovery of fragments of 
it at one place at a depth of at least 10 feet below the surface in 
bedded deposits of Pleistocene age proves that such action has gone 
on not alone in recent times. The present article deals with some 
t Published by permission of the Director, U. S. Geological Survey. 
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