1888.] PROCEEDINGS OF UNITED STATES NATIONAL MUSEUM. 447 



A SIMPLE METHOD OF MEASURING THE THICKNESS OF INCLINED 



STRATA.* 



BY CHARLES D. WALCOTT. 



When I began the study of the highly-inclined strata in Washington 

 County, K. Y., during the field season of 188G, I found it necessary to 

 measure the thickness of several sections where the surface was irregu- 

 lar, and the outcroppings of the strata numeious, though not continuous 

 on the direct line of the sections. 



Having used the Locke level in measuring horizontal strata, taking 

 the distance from the ground to the eye as the unit of measurement, it 

 occurred to me to substitute a clinometer compass for the level, and a 

 rod, instead of my body, for the unit of measure. The compass was 

 securely fastened to a light rod, so that the sights were on a level with 

 the eye when the rod was standing upright and resting on the ground, 

 and the clinometer needle at zero. The strata, in the section to be 

 measured, were inclined to the east 40°. Placing the lower end of the 

 rod at the base of the section, I inclined the rod towards the edges of, 

 and at a right angle to, the line of the dip of the strata, which was in- 

 dicated by the needle of the clinometer standing at 40°. Then, lookiug 

 through the compass sights, the point where the line of sight touched 

 the ground was marked as the next station for the rod, and on this 

 station the base of the rod was placed for the second sight, which was 

 made exactly as in the first instance, and so on to the end of the section. 

 Frequent trials were made, at the exposed outcrops, to determine the 

 angle of dip of the strata, so that the rod might be held at a right angle 

 to it. In one section of curved strata, on the mountain side, the lower 

 beds were horizontal whilst the upper beds dipped at an angle of 70°. 

 By taking into account the angle of dip of the strata, at each of the 

 measurements with the rod, so as to find the true line of sight (which 

 is the angle of the dip of the strata), the thickness of the section was 

 quickly determined. 



Each individual who attempts to measure strata in the manner de- 

 scribed should have the compass placed upon the rod just high enough 

 to bring the sights on a level with the eye, the compass being so at- 

 tached that when the rod is perpendicular the clinometer needle will 

 point to zero. 



The accompanying sketch illustrates the manner of measuring strata 

 by this method. 



liite 2 



*Read before the American Society of Naturalists, at New Haven, December 29, 1887, 



