180 BAILEY WILLIS — GRAPHIC FIELD NOTES. 



to the limited outlook in a Michigan forest, cannot well devise details of 

 methods for him who studies stratigraphy and structure on the treeless 

 plains of the west. Nor can he whose stratigraphic work in the settled 

 states is facilitated by roads prescribe methods for the investigator of volcanic 

 geology in uninhabited mountain ranges. Each must adapt to his own 

 environment the means of recording aud arranging observations, but he 

 w^ill certainly do so more intelligently if he avails himself of the experience 

 of others, whose training and experiments may contain positive or negative 

 suggestions. 



Believing this, I propose to give here for what it is worth the experience 

 of the Appalachian division of the United States Geological Survey with 

 graphic methods of mapping formations. 



Appalachian Work in the U. S. Geological Survey. — The Appalachian 

 Paleozoic province presents stratigraphic and structural problems under an 

 aspect which is familiar to all of us. Relief is seldom emphatic, heights 

 have usually struck an average elevation through successive base-leveling, 

 soil covering is the rule, vegetation flourishes everywhere, and cultivation 

 assists in obscuring geologic facts: these are obstacles to rapid work, what- 

 ever the problem. On the other hand, relief and structure are intimately 

 related as effect and cause, the factors of the problems, multitudinous as 

 they often are, are crowded together in small space, every part of the region 

 is easily accessible, roads and houses permit facilities not else available : 

 these are aids to successful w^ork. 



The geologists of the United States survey who entered this province prior 

 to 1886 were trained in western fields and did not at first devise the best 

 methods of work. The amount of geology per square mile was embarrassing 

 to them ; the facilities afifbrded by culture were not appreciated. It seemed, 

 moreover, a fair assumption that the Rogers brothers, SafiTord and others 

 had solved the geologic problems of the region and that to resurvey their 

 fields was but to confirm their results, which must be done in detail and 

 with great accuracy. Triangulation for detail was forbidden by the absence 

 of marked features of relief or culture, and meander methods were a neces- 

 sity in the absence of adequate maps. 



Stadia Transit Method. — The special conditions and the fact that the 

 purpose of the work was section-measurement led to the selection of a very 

 accurate method based on stadia measurements of distances. The instru- 

 ment used was a light transit, mounted on tripod and leveling screws, carry- 

 ing a telescope with a vertical limb and fixed stadia wires. The stadia rod 

 was 12 feet long and graduated by experimenting with a base measured by 

 a steel tape ; there were two movable targets, which were adjusted by the 

 rodman on signals from the surveyor until the interval between them was 

 proportioned to the space between the stadia wires of the telescope ; the 



