EXTEXT OF THE DENVER. 199 



unlikely that natural outcrops may occur in many places. The examination 

 of this part of the area was hurried and the routes chosen were those besi 

 calculated ti> show the extent of the formation and its limits. 



From Happy Canyon around to the creek entering the Platte ."> 

 miles suuth of Littleton, Mr. Eldridge determined the line of Denver and 

 Monument ('reek, as given upon the map, from numerous outcrops near 

 the line. On various branches of this creek the Denver beds are well shown 

 down to the crossing of the ditch, in the neighborhood of which there are 

 some very fine outcrops illustrating the variation in composition peculiar to 

 this portion of the formation, from causes now to be considered. 



The southern limit of the Denver beds on the hanks of the Platte is 

 set by the original shore-line of the horizon represented. To explain this 

 better let us recall the course of the boundary of the formation from Mount 

 Carbon, on Bear Creek, eastward. The line was found to run at first in an 

 easterly direction along the low ridge forming the south bank of Bear < 'reek, 

 and then to turn southeast, the exact course being concealed by valley 

 Pleistocene. On the eastern bank of the Platte, however, exposures have 

 been found which indicate closely where the line must cross the river. In 

 the Denver and Rio Grande Railroad cut in the ridge north of the old Platte 

 Junction the Denver beds are exposed, while in a corresponding cut in the 

 ridge to the south from that point the Arapahoe strata are clearly shown. 

 The latter also appear in characteristic outcrops in the next gulch to the 

 south and in many places along the ditch on both banks of this water course. 



SOURCES OF MATERIALS IN THE SEDIMENTS. 



The peculiar interest and importance attaching to the Denver formation 

 depend so largely upon the nature and origin of the materials composing 

 its sediments that special consideration of this point seems desirable. 



For all the sedimentary formations which we now see in this district 

 the elevated mountain masses in the Colorado Range formed the western 

 border, and it is evident that this land area must have furnished by far the 

 greater part of all rock materials in the stratified deposits. Of the other 

 shores of the Denver sea, more or less distant, it can only be assumed that 

 they were low, were themselves formed of sedimentary rocks, covered to 



