76 W. & L. E. GURLEY, TROY, NEW YORK 



FIG. 40 Vnitfd States Geological Survey llrn-li Mark. 



tablet. Always place the tablet with the axis of the stem verti- 

 cal, so that the circle marking the elevation is actually the 

 highest point of the bench mark. 



Avoid placing bench marks on new or unstable structures. 

 Wherever possible, place the bench mark so that the gage may 

 be reached in one set up. 



Having established the station bench mark, its location with 

 respect to prominent objects should be carefully described. 

 While in some cases it may be desirable to know the elevation 

 of the gage datum above sea level, much confusion will be 

 avoided if an arbitrary elevation, applicable to all emergencies 

 and future conditions, is assigned, and only that elevation used 

 in station descriptions. 



