206 APPENDIX. 



account, it is altogether unwarrantable to speak of the "Kasaoli ridge as a branch of the 

 great Himalayan range," which range is described as " bending round to terminate in the 

 plains at Nahun." Or again, to apply the same term to the Himalayan range, and the Simla 

 range, when by the latter is meant the exceedingly tortuous watershed from Kasaoli to the 

 snowy peaks of Kunawur, right across the strike of the whole series of Himalayan and Sub- 

 Himalayan series of rocks, is also unwarrantable, the intrinsic significance of the two being 

 as different as it could well be.* 



I have still to notice the influences by which the uniform action of the two active agents 



of hill-formation are modified. In any actual case the mass 

 Modifying influences. 



acted on will be very far from homogeneous, or even symmetri- 

 cally heterogeneous. Any considerable area and thickness of the earth's crust is sure to 

 present rocks in many different conditions of induration, and presenting various degrees of 

 resistance. We know too that different systems of disturbance have, at different times, 

 affected the same area, so that the ultimate position of any rocks that have undergone a 

 number of such vicissitudes, will be the resultant of all these separate movements. It is 

 certain that the minor phenomena of any great operation of elevation must be largely modi- 

 fied by these passive influences. In the results of denuding forces, however, these influences 

 become of still greater, indeed of chief, importance. A hard band of rock, into whatever 

 position it may have been pushed by repeated elevation and crushing, will inevitably weather 

 into a ridge. It is easy to conceive these conditions so accumulated that in any great system 

 of elevation large areas, not immediately contiguous to the lines of maximum effect, may 

 show but little regularity in the arrangement of the rock masses. In such a case the 

 heterogeneousness of texture and of structure may be so exaggerated that it practically 

 becomes on a large scale homogeneous agaiD, and the drainage system, resulting from the 

 denudation of such a mass, assimilates more to the transverse or denudation type of origin 

 than to the elevatory, in which longitudinal lines are well marked. 



* The errors of the map-maker are even more important to the geologist than those of the tourist, for with 

 the work of the former he cannot dispense. I have often endeavoured to impress upon surveyors the impor- 

 tance of their knowing something of the structure of what they attempt to represent. The reply that one 

 can do no more than copy correctly, or one cannot know everything, can scarcely be accepted as satisfactory. 

 Under the impossiblity of making one anything like a perfect machine, the only safe plan is to make him less 

 a machine. We all know in what a loose sense the word copying must be applied to much of the process of 

 the best map-making ; but, surely, knowledge would be a safer guide than preconceived ideas in this the 

 artistic element, which is supplementary to the purely mechanical part of the surveyor's work. The little errors 

 that are occasionally found in the admirable map with which I worked in the north-western Himalaya are 

 such as could not have occurred, had the surveyor possessed even a general knowledge of mountain formation 

 from the observations that he could not then have failed to make in the prosecution of his work. 



Calcutta, January, 1864. 



