372 Proceedings of the Royat Society. 
throw out the idea, that the structure in question may perhaps be 
explained by your views on the zoned structure of glacier ice, the 
layers of less tension being, in the case of the Ascension obsidian 
rocks, rendered apparent, chiefly by the crystalline and concretionary 
action superinduced in them, instead of, as in zoned ice, by the con- 
gelation of water. “ = * 
‘«« How singular it at first appears, that your discoveries in the 
structure of glacier ice should explain the structure, as I fully believe 
they will, of many volcanic masses. I, for one, have for years been 
quite confounded whenever I thought of the lamination of rocks which 
have flowed in a liquified state. Will your views throw any light 
on the primary laminated rocks? The lamine certainly seem very 
generally parallel to the lines of disturbance and movement, Be- 
lieve me, &c. C. Darwin.” 
To Professor l'ORBES. 
Professor Forbes confirmed the previous remarks by others, made 
by himself on the specimens transmitted to him by Mr Darwin, and 
on specimens from Lipari and Iceland in the collection of the Royal 
Society, as well as by direct observations made by himself on the 
lava streams of AXtna. 
3. Professor Forbes then read the following Letter from 
Professor Gordon, of Glasgow, also on the subject of 
the Viscous Theory of Glaciers. 
GuLasGow, January 31. 1845, 
* * * When you requested me to give you a memorandum of 
what appeared to me to be the very glacier-like motion and appearance 
of Stockholm pitch flowing from a barrel, I considered my observation 
to have been too casual to be worth writing, and having foreseen that 
I could arrange an experiment at Gateshead in the beginning of the 
year, I delayed giving you the memorandum you wished. I had 
hoped to have been able to inspect and report on my experiment 
about this time ; but I cannot go to Gateshead for some time to come, 
nor have I had any report of the progress of my pitch glacier since 
the 6th January, when I was informed it had not moved since the 
day after I left it, on the 28th December. Your note of yesterday 
induces me to offer you the following still perfectly vivid impressions 
of the analogy between ice and Stockholm pitch. 
Allow me, in the first place, to mention that I read your travels in 
the Alps, in May last ; and that on the 24th of June I spent almost 
20 hours on the glaciers of the Grindelwald. I went up by the 
lower glacier, prepared with poles to prove the motion, and actually 
observed a progress of about 12 inches in the course of 13 hours, 
from 6 a.M. to 7 p.m. I traced the “dirt bands” on the surface. 
