MAP SECTION OF TERTIARY STRATA 



269 



boundary in general is easily followed, because of its usual occurrence at 

 the base of prominent cliffs. On tlie other hand, the base of the Dawson 

 arkose in places can be followed only with difficulty, and in areas of low 



DENVER 



DAWSON ARKOSE 



LARAMIE 



Figure 1. — Map and flection of Tertlanj strata hctircen Denver and Colorado Sinings 



relief, as on the plains, the contact is generally concealed by Quaternary 

 deposits, so that its location can only be inferred. But where better ex- 

 posed, as northeast of Perry Park, in the Castle Uock quadrangle, the 



