THE IMAGINARY RANGE AND TROUGH. 



55 



The underground form of the trough cannot be determined by 

 surface observation of a geological character, and the readiest 

 means of applying the geodetic results to the solution of this prob- 

 lem appeared to be the calculation of the effect of a series of troughs 

 of various forms and dimensions, by the combination, of which a 

 series of cross sections could be built up and the calculated com- 

 pared with the observed results. This has been done in tables 14 

 to 16 ; in table No. 14 (page 54) a width of 50 miles is assumed 

 and we have the deflections which would be produced if it had a 

 uniform depth with vertical sides, if it had vertical sides and a floor 

 sloping upwards from a depth of 15,000 ft. on the north side to 

 10,000 ft. at the south, and if it had a vertical side on the north and 

 a floor sloping gradually upwards to the surface at the southern edge. 

 Table No. 15 gives the deflections which would be produced by a 



Table 15. — Deflections due to a trough 100 miles broad of various 

 sections ; density -8 of average rock. 





Uniform 



DEPTH. 



Depth varying FROM TO 



Station. 











10,000 feet. 



15,000 feet. 



10,000 feet. 



15,000 feet. 



— 10 



















— 9 







— 1 







— 1 



— 8 



— 1 



— 1 



— 1 



— 1 



— 7 



— 1 



— 2 



— 1 



— 2 



_ 6 



— 2 



— 3 



— 2 



— 2 



— 5 



— 3 



— 4 



— 2 



— 3 



— 4 



— 3 



— 5 



— 3 



— 4 



— 3 



— 4 



— 7 



— 4 



— 5 



— 2 



— 6 



— 10 



— 5 



— 7 



— 1 



— 9 



— 14 



— 7 



— 11 







— 21 



— 29 



— 18 



— 25 



+ 1 



- ,9 



— 13 



— 5 



— 7 



+ 2 



— ffi 



— 8 



— 1 



— 1 



+ 3 



"I 3 



— 5 



+ 2 



+ 2 



+ 4 



-12 



— 2 



+ 3 



+ 5 



+ 5 











+ 4 



+ 6 



+ 6 



+ 2 



+ 2 



+ 5 



+ 8 



-f 7 



+ 3 



+ 5 



+ 6 



+ 8 



4 8 



+ 6 



+ 8 



+ 6 



+ 9 



+ 9 



+ 9 



+ 13 



+ 6 



+ 9 



+ io 



+ 21 



+ 29 



+ 6 



+ 9 



trough 100 miles in width, of uniform depth, or with a vertical side 



[ 203 ] 



