Correspondence—Prof. T. G. Bonney. 329 
Consequently the heated rocks, if hitherto kept solid by pressure, 
would enter into fusion at somewhere about this melting tempera- 
ture, when the pressure was thus removed. I was the first to 
point this out in 1868. It would seem then that the isotherm, 
corresponding to the melting temperature at the surface, will near 
about determine the thickness of the permanently solid crust. 
Again, if a fracture were to be opened from below upwards, as 
might happen in any portion of a synclinal trough, or less advantage- 
ously from above downwards in an anticlinal; or if three or more 
faults radiating from a central vertical, combined with a slight 
horizontal shift, were to occur; then a funnel would be formed 
communicating with these hot rocks, and reducing the pressure at 
that spot nearly to the atmospheric pressure. Immediately the super- 
heated rocks, which probably contain superheated water, if not 
already fluid, would enter into fusion. Steam would rush upwards, 
and lava would follow it; and although statical pressure could not 
perhaps carry this quite to the surface, yet the momentum, acquired 
by the molten rock in flowing towards and up the funnel, would 
for a while carry it still further, so that an overflow of lava would 
take place. But when this momentum was expended, it would sink 
back again into the funnel. 
I have formerly offered some speculations upon these and kindred 
subjects, fairly open perhaps to the charge of “imagining that I 
have created a mathematical theory for phenomena.” They are 
contained in three papers published in the Cambridge Philosophical 
Society’s Transactions—viz. “ On the elevation of mountains by 
lateral pressure, with a speculation on the origin of volcanic action”: 
1868.! “On the inequalities of the earth’s surface, viewed in con- 
nexion with the secular cooling”: 1873. And, ‘“ On the inequalities 
of the earth’s surface as produced by lateral pressure, upon the 
hypothesis of a liquid substratum”: 1875. These have been all of 
them placed in the library of the Geological Society. 
Haruton, 8th June. O. FISHER. 
THE ‘“‘ PRE-CAMBRIAN”’ ROCKS OF ROSS-SHIRE, 
Str, —Now that Dr. Hicks has completed his notice of the Ross- 
shire rocks, I must ask permission to make one or two comments, 
since the union of Mr. Davies’s name with his own naturally 
strengthens his case. Mr. Davies’s support, however, I venture to 
say, is more apparent than real; for in some respects no one disputes 
the conclusion ; in others Mr. Davies speaks with reserve; while in 
others the evidence does not appear to me to have been fully placed 
before him. 
I will therefore recapitulate the points in Dr. Hicks’s original paper 
(Q. J. G. S. vol. xxxiv. p. 811) which I controverted in my notes 
upon the district (Q. J. G. S. vol. xxxvi. p. 93) :— 
1. He represented the so-called syenite in Glen Laggan as intru- 
sive in the quartzite and limestone series. I asserted that this rock 
in the main was not igneous and was not intrusive, but brought up 
by faults. Dr. Hicks still maintains that it is igneous, but now claims 
1 Reviewed in Watwre, vol. v. p. 381. 
