OKIGIN OF THE DIKES. 229 



rial filling fissures, varying from mere films on cleavage planes of ortho- 

 clase grains in the granite to dikes several hundred yards in width, could 

 have resulted from infiltration. 



It has been stated above that the belt of observed dikes lies adjacent 

 and parallel to the Manitou park basin of sedimentary rocks, the princi- 

 pal element in which is the red sandstones and grits of the Carbonifer- 

 ous (?) or Trias (?). These beds are, however, of much coarser and more 

 heterogeneous character than the dike-rock, and the observations made 

 do not suggest that the proximity is anything more than accidental. It 

 is not known that the dikes are younger than the sediments, for they 

 were nowhere found in contact. The strata of the basin are now seen at 

 the same level with the dikes, but ftiulting and a synclinal fold have 

 clearly lowered them with reference to the granite on either side. Finally, 

 it is probable that the dikes are not limited to the vicinity of the sedi- 

 mentary basin. Neither end of the belt containing the dikes was de- 

 termined, and an observation by Professor G. H. Stone shows plainly 

 that sandstone dikes do occur in the same general strike line and far 

 removed from any sedimentar}^ rocks. 



Professor Stone '''•'^ lias published a short note on '• The Turkey Creek 

 Mining District, El Paso county, Colorado," which lies to the southeast 

 of Pikes peak, in th-e granite mountain area and several miles from the 

 border of the plains. The locality is about eighteen miles a little east 

 of south from the southernmost dike observed by tlie writer. Referring 

 to the principal lode, Professor Stone describes it as follows : 



" It is a narrow strip of i)ink or reddish rock that outcrops at intervals and lias 

 been located for about 12 miles. Its direction is nearly north and south. It is 

 bordered on both sides by granite-gneiss and other Archean rocks. To the unas- 

 sisted eye this so-called lode often presents the compact apj^earance of an igneous 

 rock, ])ut examined in thin section under the microscope it is plainly seen to be 

 a fine-grained sandstone. The grains are of quartz. They are nearly all well 

 rounded, and their interstices are filled with an iron-rusty cement. In places the 

 grains are larger, some one-sixteenth of an inch in diameter, and easily recogniz- 

 a])le by the eye." 



Through the courtesy of Professor Stone the writer has been able to 

 examine a thin section of this '* lode " rock, and it is, as would appear 

 from the above description, identical in character with the dike-rocks to 

 the north of Pikes ])eak. If then the Turkey creek rock belongs to the 

 dike system described in this paper, it is unlikely that the latter has any 

 direct connection with the sedimentary rocks of Manitou park. Further 



♦Engineering and Mining Journal, September 9, 1893. 



