Reviews — Reversed Fault near Kotli, Jammu Province. 565 



A valuable feature of the book is the fullness of the references to 

 previous literature, which appear at the end of eacli chapter, and 

 again, in alphabetical list, at the end of the volume. 



P. L. 



II. — On the Inclination of the Thrust-plane or Reversed Fault 



BETWEEN THE SlWALIK AND MuRREE LlNE OF FORMATIONS NEAR 



Kotli, Jammu Province. By C. S. Middlemiss. ltec. Geol. 

 Surv. India, vol. 1, pp. 122-5, pi. xxviii, 1919. 



IIS" the Geological Magazine for 1903 (pp. 305-6) Mr. Lake 

 published a very short paper on " The Circular Form of 

 Mountain Chains". In this paper Mr. Lake showed that if Suess' 

 conception of mountain chains as the crumpled edges of flat-based 

 earth-scales is true their intersection with the surface must always 

 be an arc of a circle ; furthermore, he pointed out that the angle 

 which a plane makes at its outcrop with the surface of the sphere is 

 equal to the angular distance measured on the surface of the sphere 

 between the centre and circumference of the circle formed by the 

 outcrop of the plane. Mr. Lake went on to say, " If I were to 

 attempt, on this view, an ideal representation of the Himalayas, 

 I should draw, some little distance below Middlemiss' Section YI " 

 (referring to a paper in Mem. Geol. Surv. India, vol. xxiv, pt. ii), 

 " a thrust-plane making an angle of 14° with the horizontal." 



It has hitherto been customary in drawing ideal sections of the 

 Himalayas to represent fold-faults of this category as having steep 

 inclinations, usually something between 45° and 60° with the 

 horizontal, and Mr. 11. J). Oldham even speaks of the main boundary 

 fault as being "a nearly vertical plane of separation" (Mem. Geol. 

 Surv. India, vol. xlii, pt. ii, p. 4). 



As described in the paper quoted at the head of this review, 

 Mr. Middlemiss has plotted with great care on the new contoured 

 1 in. map of Jammu and Kashmir the plane of division between 

 the younger zone of Siwalik rocks and the older Murree zone below. 

 This plane can be traced with great accuracy owing to the strong 

 colour-contrast between the two series. The course of the fault 

 when thus plotted, as shown on the map accompanying the paper, 

 makes two very distinct V-shaped upstream bends, and by using the 

 data thus afforded Mr. Middlemiss has calculated that the actual 

 angle of dip of the plane is from 12° to 15° with the horizontal. 

 This affords a remarkable confirmation of the soundness of 

 Mr. Lake's reasoning and is a valuable instance of the untrust- 

 worthiness of inferences drawn from field-observation without 

 accurate mapping to scale. 



III. — The Magnesite Deposits of Bulong. By F. B. Feldtmann. 

 Bull. 82, Geol. Survey Western Australia, pp. 38, with 2 

 plates and 7 figures. Perth, 1919. 



f MHIS Bulletin gives the results of a recent exploration, stimulated 

 J_ by war conditions, of deposits of magnesite in the North- 

 East Coolgardie Goldfield, together with a general account of the 



