J56 



BOTANICAL GAZETTE 



[SEPTEMBER 



Range. This has been studied by many geographers, more recently 

 by Davis. The Front Range has been described by him as a sub- 

 maturely dissected upland of crystalline rocks, elevated above the 

 plains to the east by a long north-south monoclinal fold. The 

 tops of most of the hills form the remains of a peneplaned surface, 

 the result of the erosion following the uplift, with complete removal 

 of the sedimentary layers from the raised area on the west. A few 



Fig. 2.— Davis' block diagram of Front Range (reproduced with author's per- 

 mission from i): at right is condition following first uplift with monoclinal fold; 

 next part shows peneplaned upland with monadnocks and cuestas (hogbacks) ; third 

 shows entire region after second uplift; last block on left shows present condition, 

 with glacier-carved range-crest, gently sloping, dissected, crj'stalline upland, of which 

 lower and eastern part forms foothills, and mountain-front, with sloping crags, cuestas, 

 and longitudinal vallej's; outside may be seen debris-covered terraces and broad 

 valleys of streams running out into plains. 



monadnocks surmount the general level. The present eastward 

 inclination of the old peneplain and its dissected character in the 

 crystalline area, and the removal of sedimentary strata of the 

 plains to a depth far below the foothills, are the effects of a second 

 uplift, an uparching of the whole region, and of the subsequent 

 cycle of erosion. Near the base of the original fold the sedi- 

 mentary strata are sharply upturned against the outer granitic 

 slopes, the ends of the resistant strata forming ridges and sloping 

 crags (fig. 2). 



