METHOD OF USING THE STADIA TRANSIT. 181 



number of divisions on the rod included between the targets then corre- 

 sponded to the distance from transit to rod. The maximum distance 

 measurable with this instrument and rod was 1,500 feet. A much greater 

 reach might have been obtaiued with a longer rod, but it was not deemed 

 desirable. 



The operation at any one statiou was as follows : the geologist set up and 

 leveled his transit, received from the rodman the distance reading of the last 

 sight and platted his topographical and geological notes accordingly. The 

 rodman set a target to the height of instrument and went on to select the 

 next station. When ready the rodman called, the geologist observed and 

 noted the course and slope of the new sight, by signals adjusted the targets 

 to the stadia wires, and then rejoined the rodman. 



By repetitions of this process, with more or less delay for misunderstandings 

 on account of the distance frequently separating the geologist and rodman, 

 the meander line progressed at the rate of 3 to 6 miles a day. 



The record consisted of two parts containing similar information : the one 

 part composed of figures and verbal notes; the other part representing ap- 

 proximately the map to be platted from these figures. The final interpreta- 

 tion of the whole record constituted the ofl[ice work. 



This required for each sight the reduction of slope distance to its horizon- 

 tal projection and a calculation of elevation of each station. The course and 

 distance being platted, the geologic facts could be indicated and the sections 

 developed. This labor proved very onerous ; unnecessary mechanical accu- 

 racy of delineation absorbed time that should have been given to thoughtful 

 study. The end in no sense justified the means, for the method was adapted 

 to the accurate coordination of a mass of facts in a small area, as in a min- 

 ing survey, not to generalizations in stratigraphy and structure. 



Adoption of graphic Methods. — It has already been stated that the record 

 of stadia work was in two forms : the one numerical, the other graphic. The 

 former occasioned most of the office work, the latter contained the pith of 

 the geologic information. It followed that in casting about to devise a 

 method for mapping formations, we sought to get rid of the figures and to 

 improve the sketch to the standard required for a final plat fit for transfer 

 to the map. To do this required the adoption of some means other than the 

 stadia of measuring distances, and of means for sketching directions and dis- 

 tances more accurately than had previously been done. 



For measuring, two instruments have been successfully used : the one the 

 wheel of a buckboard or sulky with some attachment for marking its revo- 

 lutions ; the other a pair of legs, usually those owned by the geologist. With 

 the former the unit of measurement is a "wheel," i. e., the circumference of 

 the wagon wheel ; with the latter the unit is a pace, a function of the indi- 

 vidual. These vary in different instruments and require reduction to a com- 

 mon scale before combining different pieces of work. 



