44 



Correspondence — Cayt. F. W. Sutton. 



OOIR-I^ESIF'OI^ZDlEn^CIE]. 



SUGGESTIONS FOR GEOLOGICAL SUEVETORS. 

 Sir, — The following proposition will, I venture to think, be found 

 very useful to Geological and Mining Surveyors, for none of the 

 text-books give any information on the subject. I hope, therefore, 

 that you will be able to find room for it. E. W. Hutton. 



Wellington, New Zealand, 

 Uh August, 1873. 



Given the dip on each side of an anticlinal or synclinal curve, to 

 find the direction of the axis. 



(a.) To find the bearing of the axis. 



Let C and OB represent the bearings of the two dips. From 

 erect the vertical OD. Make the angles OCD 

 and OBD equal to the dip on each side of the 

 curve. Draw CA at right angles to OG, and 

 BA at right angles OB. Join AO and BC. 

 Then CA and BA represent the strike of the 

 beds on each side, and A represents the bearing 

 of the axis. 



Let ^ OCD = d; /_ OBB — dl; /_ OAC=x; 

 /_ OAB-=x; and Z.BAC = A = x\x'. 

 Then because OBE and CEA are similar tri- 

 angles Z. OB C= X ; and for the same reason 

 Z OCE=x'. 



Also CO = 1)0 cot d 

 and BO = BO cot d'. 



Consequently 



tan ^ (x' — x) = 



(cot d' — cot d) tan -^ A 



cot d' -f cot d. 

 by which x, and therefore the bearing of the axis, can be found. 



(b.) To find the inclination of the axis. 



Let, as before, A C represent the 

 strike, and JDCO the angle of dip 

 {d) of the beds on one side of the 

 curve. Join A B. Then A repre- 

 sents the bearing of the axis, and 

 BA is its inclination to the horizon. 

 Let ^ BAO = y. 



BO 



Then tan y = -tq. 



B0= DC tan d 



A0=: DC cosec x 



tan d , . 



/. tan y = ■ = tan d sm x. 



^ cosec X 



which gives the inclination of the axis with the horizon. 



N.B. — The axis of an anticlinal curve will incline downward 



towards the angle formed by the two lines of strike, while the axis 



of a synclinal curve will incline upwards towards that angle. 



