BULLETIN OF THE GEOLOGICAL SOCIETY OF AMERICA 



Vol. 5, pp. 225-230, PL. 8 FEBRUARY 23, 1894 



INTRUSIVE SANDSTONE DIKES IN GRANITE ^^^ 



BY WHITMAN CROSS 



{Read before the Society December 28 ^ 1893) 

 CONTENTS 



Page 



Introductory 225 



Region of Occurrence 225 



Characteristics and ]Mode of Occurrence 226 



The Dike-rock 227 



Origin of the Pik(\< 228 



hitroductorij. — The phenomenon to be described in the following pages 

 is that of the occurrence of sandstone — a rock composed of worn sand 

 grains— as the filling of an extensive system of fissures in granite and- 

 under circumstances indicating that the sand was forced into the fissures 

 under great pressure. 



Region of Occurrence.— The sandstone masses in question occur in the 

 Pikes peak region, in Colorado, and were discovered in the course of a 

 geological survey of the district during the past summer of 1893.t The 

 dikes observed are limited to a belt about ten miles long and one mile 

 wide, with a trend north-northwest to south-southeast, the southern end 

 of wliiqlY is about five miles north of Pikes peak. This belt lies on the 

 western side of the narrow Manitou park basin of sedimentary rocks, at 

 a distance six to eight miles west from the border of the Great plains, 

 and 1,500 feet above them. 



* Printed by permission of the Director of the United States Geological Survey, 

 t Prior to entering upon the field-work Professor G. H. Stone, of Colorado Springs, called the 

 writer's attention to tlie occurrence of isolated sandstone bodies in the Pikes peak granite area, 

 the origin of which was not known to him. Some of the masses referred to by Professor Stone 

 were found to be dikes, while others were of entirely different character. In the field study of the 

 dikes Mr E. B. Mathews, Fellow in Johns Hopkins University, took part, as geological assistant. 



XXXI— Bum,. Gkof,. Sor. Am., Vol, 5, 1893. (225) 



