It appears to me that the possibility of error in this argument lies in the omission of all consideration of the migration of divides and the resulting adjustment of stream courses to deep internal structure; but at the time of the exploration of the Colorado river, this important process in the development of rivers was not understood. It now seems only natural that the original, consequent, cataclinal streams, flowing down the slopes of the range from crest to flanks, should have permitted the opening of subsequent monoclinal branches on the soft beds that they discovered; and that the shifting of divides in these monoclinal valleys should have led to the capture of several cataclinal streams by that particular one of the subsequent branches that grew out from the master stream, the Green river itself. Thus it must happen that the streams "which head near the summit of the range, and, running down the flank, turn into the Green river, are, in their upper courses, cataclinal, and when they turn to follow the strike of the rocks into Green river, are monoclinal" (161): this being a normal result of river work in cutting down the thousands of feet of rocks of various hardnesses, here concerned. The smaller streams of the Uinta range are therefore certainly not of necessity antecedent to the Uinta uplift: the probability is that they were originally purely consequent, and that at present they are nicely adjusted to the structures that they have discovered. I have learned so much from the doctrine of baselevelling, as presented in Major Powell's writings, that I shall hope to profit by the lesson of the Uinta drainage as well: that is, the possibility that an apparently sound conclusion may be overturned when new processes that bear upon it are discovered. It is here said that the drainage of the Watchung crescent in New Jersey is an example of partial adjustment following a superimposed origin: hence the necessity of watching closely for the discovery of new principles in the history of river work that may call for a revision of this conclusion.