LETTER. 13 



whenever the stratigraphical conditions have been observed, and are 

 known, a map showing the elevation curves will enable the geologist to 

 recognize, with great accuracy and certainty, details of geological distri- 

 bution that otherwise would require considerable time and labor to 

 work out. 



In working out sections the curves are of importance, giving the 

 geologist a means by which to give a correct diagram of the line of 

 country through which he has made his section, and furthermore fur- 

 nishes him valuable data facilitating the measurement of strata. 



The map of the sources of Snake River and its tributaries, on a scale 

 of five miles to one inch, is a most valuable contribution to the geogra- 

 phy of a portion of our western country, previously almost entirely 

 unknown. The great amount of faithful, conscientious labor bestowed 

 upon it by Mr. Bechler, both in the field and in the office, is so evi- 

 dent that I need not speak of it in detail. An edition of the drainage 

 I)ortion, with the brush-work omitted, will be published during the sum- 

 mer, showing the geological formations with colors, by Professor Brad- 

 ley. During the summer of 1872 Mr. Bechler resurveyed the Upper 

 and Lower Geyser Basins of theFirehole Eiver; and the two charts, on 

 a scale of six inches to one mile, have just been very beautifully en- 

 graved on stone by Mr. Bien. 



It is believed that all unkind criticisms of the labors of other scien- 

 tific men are out of place in an official report, and in no instance will 

 they receive the sanction of the geologist in charge. Each assistant is 

 held responsible for the correctness of his statements in his report, and 

 it is presumed that his love of truth is superior to his personal feelings. 

 Problems are arising and will continue to arise about which there will 

 be difference of opinion among true men of science. We shall accei)t 

 the verdict founded on the evidence as soon as it comes fairly before 

 us, regardless of our preconceived opinions. 



In performing so great an amount of field-work, and in publishing so 

 freely and rapidly as we do, an unkind critic may find defects in our 

 reports which might not have existed with delay ; but it seems not only 

 necessary but eminently desirable to bring our results before the public 

 at as early a date as possible. Should mistakes occur, (and they cannot 

 reasonably be avoided,) we hope to correct them in future publications. 



I regret that my own report has not beenioore carefully prepared this 

 season, and that I have been obliged to omit several chapters in which 

 I had intended to discuss some of the more important problems in the 

 geology of the Eocky Mountain region. 



The discussion of the Lignitic group will be continued by Professor 

 Lesquereux. His views in regard to the age of this group are well 

 known, and it seems probable that they will be sustained by future evi- 

 dence. The stratigraphical evidence on this subject, so far as Colorado 

 is concerned, will be subjected to the closest scrutiny the present season. 



The present report of progress is submitted with the belief that it is 



