Abstract

Introduction

Several years ago, while studying the Cretaceous shales upon the northwestern border of Sacramento valley in California, I observed in a stream bed a number of large fragments of sandstone. They were carefully examined for fossils, in the belief that the rock from which they were derived was regularly interstratified with the Cretaceous shales. Near by I discovered an excellent exposure of a vertical dike cutting through the bank of tilted shales from top to bottom, in plain view for a distance of 60 feet. When I reached the dike and found it to be composed of sandstone, the same I had examined for fossils, my interest was thoroughly aroused. A sandstone dike seemed a paradox. Further search in that region brought other dikes of the same nature to light, but the puzzle was not investigated until last summer, when, with the aid of Mr. J. Stanley-Brown, a geologic . . .

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