20 National GeografJdG Magazine. 



it is worn down to a featureless base level surface, are worthy of 

 the most attentive study. The immaturity of the broken country 

 of southern Oregon, as compared with the more advanced forms 

 of the Basin ranges, is a case in hand. The Triassic formation 

 of the Connecticut va'lley is in some ways of similar structure, 

 being broken by long parallel faults into narrow blocks or slabs, 

 every block being tilted from its original position. Russell's de- 

 scription of the blocks in southern Oregon would apply nicely to 

 those in Connecticut, except that the former have diverse dis- 

 placements, while the latter all dip one way ; but the Connecticut 

 individual has, I feel confident, passed through one cycle of life 

 and has entered well on a second ; it has once been worn down 

 nearly to base level since it was broken and faulted, and subse- 

 quent elevation at a rather remote period has allowed good ad- 

 vance in a repetition of this process. The general uniformity in 

 the height of its trap ridges and their strong relief above the 

 present broad valley bottom, require us to suppose this complex- 

 ity of history. A given structure may therefore pass through 

 two or more successive cycles of life, and before considering the 

 resulting composite history in its entirety, it would be best to 

 examine cases of simple development in a single cycle. After 

 this is accomplished, it would be possible to recognize the incom- 

 plete partial cycles through which a structure has passed, and to 

 refer every detail of form to the cycle in which it was produced. 

 The most elementary example that may be chosen to illustrate 

 a simple cycle of geographic life is that of a plain, elevated to 

 a moderate height above its base level. The case has already 

 been referred to here and is given in more detail in an article 

 printed in the proceedings of the American Association for the 

 Advancement of Science, for 1884, to which I would now refer. 

 When the succession of forms there described as developed at a 

 given elevation over base level is clearly perceived, the occurrence 

 of forms dependent on two different base levels in a single region 

 can easily be recognized. The most striking example of such a 

 complex case that I know of is that of the high plateaus of Utah, 

 as described by Dutton. Northern New Jersey pi-esents another 

 example less striking but no less valuable : the general upland 

 surface of the Highlands is an old base level, in which valleys 

 have been cut in consequence of a subsequent elevation. The 

 plateau developed on the tilted Triassic beds about Bound Brook 

 is a second base level, cut during a halt in the rise from the 



