WILSON ON GEOGRAPHICAL WORK OP THE SURVKY. 733 



tended south and west. Station 30 to Engineer Mountain, distant 

 6.98 miles, a fall of 920 feet, the mean of eight determinations, 

 range 22 ; thence west to station 36, distant 6.76 miles, a fall of 

 417 feet, the mean of eleven determinations, range 51 ; thence to 

 station 37,' distant 3.65 miles, a rise of 94 feet, the mean of five 

 determinations, range 35. Another important sub-line extends from 

 Sultan Mountain to the northwest. The first link in the chain is the 

 line from this point to station 28. The heights of stations 30 and 16 

 above Sultan Mountain having been already well determined from the 

 central chain, I made use of all the connections between station 28 and 

 each of these points, reducing all of them to a common point. The re- 

 sult from this was the following : Sultan Mountain to station 28, distant 

 7.86 miles, a fall of 484 feet, the mean of eighteen determinations, range 

 76 feet ; thence to station 9, distant 3.77 miles, a rise of 324 feet, the 

 mean of eight determinations, range 43 feet; tbence to Mount Sneffels, 

 distant 5.94 miles, a rise of 952 feet, the mean of six determinations, 

 range 36 feet; thence to station 34, distant 6.65 miles, a fall of 1,161 

 feet, the mean of five determinations, range 23 feet. This completes all 

 the well-determined chains. Other stations on which barometric read- 

 ings have been taken were connected with as many points in the main 

 lines as possible, and these being reduced to a common point, a mean 

 was taken. Such points are tbe following : Sultan Mountain to station 

 10, a fall of 223 feet, the mean of eleven determinations, range 76 feet ; 

 Uncompahgre Peak to station 5, a fall of 1,498 feet, the mean of ten de- 

 terminations, range 85 feet; Uncompahgre Peak to station 11, a fall of 

 3,624 feet, the mean of eight determinations, range HI feet; Sultan 

 Mountain to station 51, a fall of 835 feet, the mean of three determina- 

 tions, range 75 feet; Sultan Mountain to station 48, a fall of 1,061 feet> 

 the mean of six deterannations, range 59 feet ; Hardie's Peak to station 

 13, a fall of 1,175 feet, mean of fore and back sights, range 6 feet. Be- 

 sides these, there are two which depend on single determinations. 

 First, from Sultan Mountain to the point in Baker's Park where the 

 road crosses Cement Creek in Silverton, distant 3 miles, a fall of 3,961 

 feet; second, from Mount Sneffels to station 32, which is obtained from 

 sights to a common point between them, distant from Mount Sneft'els 

 2.04 miles, and from station 32,3.75 miles, the fall is 5,050 feet. This 

 difference of level is checked by sights to distant points to the south of 

 station 32. These two cases are admitted because the distances were 

 80 short as to i)reclude the possibility of any considerable error. From 

 these results a table was made out showing the heights of each station 

 above or below a common datum point. Sultan ^Mountain was selected 

 as the datum point from its central location, and also from the fact that 

 it was situated on the great central chain of levels, at its juncition with 

 two principal sublines. A second column was added, giving the height 

 of each station as determined by the single barometric reading taken 

 thereon. A third column was made out of the first two, by adding the 



