16 Rey. O. Fisher on Deflexions - 
out of the compression of a crust 25 miles thick, and that by 
far the greater volume of the crushed-together mass went 
down into the denser substratum upon which it is supported 
by isostacy. I take the density of the crust rock to be 2°68 
(that of granite), and that of the substratum to be 2°96 (that 
of basalt). The consequence of this arrangement will be 
that the “root”? of the plateau would dip about 29 miles * 
into the substratum, and that the root of the inclined plane 
of the outer ranges would be represented by an inverted 
plane having an angle of 24° 31! 5", 
Major Burrard has calculated by the method of compart- 
ments the deflexions which the mountains might be expected 
to produce at various stations in the meridian of Kalianpur, 
and at p. 94 of the Report he has given a table containing 
an analysis of the calculated deflexions, separating the com- 
ponents of the deflexion due to the Himalaya from those 
due to other areas. This affords a criterion as to what extent 
our assumption respecting the form and position of the visible 
mass represent for our purpose the actual high land. Major 
Burrard has assumed 2°65 to be the density, while I have 
taken 2°68, to agree with the value used in ‘ Physics of the 
Karth’s Crust, but the discrepancy is immaterial. 
My calculations give the deflexions in a direction perpen- 
dicular to the range, and not in the meridian, and it is not 
easy to say what ought to be taken as the inclination of the 
range to the meridian of Kalianpur. Referring to Mr. Old- 
ham’s map of the Himalayas in his ‘ Geology of India,’ it 
seems as if we may consider it about 45°. Hence the de- 
flexions in the Report being given for the meridian, we may 
* This depth assumes exact isostacy. It appears very great, and: it 
might be asked whether a less amount of protrusion of the root into the 
substratum would not suffice. But the Himalaya Mountains appear to 
be rising, as is shown by the enormous quantity of detritus which they 
furnish. This would point to the depth of the root being maintained too 
great for isostacy rather than too small: indeed, it may extend beyond 
the foot of the slope and beneath the plains, which are above the sea- 
level. 
“Ever since our great pioneer in Himalayan geology, Mr. Medlicott, 
first examined and described the sub-Himalaya in his memoir (Mem, 
Geol. Surv. of I. vol. iii.) and since the Rev. O. Fisher wrote his far- 
seeing ‘ Physics of the Earth’s Crust,’ it has been gradually becoming 
evident to all who really examine the question in detail, that the Hima- 
laya are and have been in a constant state of change: a state of 
elevation along the main axis and depression along the mountain foot, 
with intermediate zones of crushing, crumpling, and over-riding along 
shear and thrust planes. This is so evident that, if one desired to be 
very particular, one might say literally that the Himalaya of to-day are 
not the same as those of yesterday.’”—Memoirs of the Geological Survey 
of India, vol. xxvi. by C. S. Middlemiss, p. 285. 
