OSS S—“<—~;PSPhté‘(C;C;SCS 
On the Viscous Theory of Glaciers. 373 
I was let down into several crevasses, one of them to a depth of 30 
fect, and could trace the slaty st»uctwre of the ice, the alternate 
clear blue thin veins, and the transition to opaque grey or even 
white. I descended from the glacier with a much better appreciation 
of the theory of glaciers than I had had, and a strong conviction 
that the facts I had observed, could not be otherwise accounted for 
than by the mechanical theory you have given. In passing through 
Gateshead in August, a broken headed barrel of Stockholm pitch at 
the Wire Rope Factory, attracted my attention. Its general appear- 
ance is represented in Fig. 1.* 
A mass of Stockholm pitch broken from a barrel in August (at 
the time of the observations I am about to mention) presented a dark- 
brown colour, a glassy lustre, translucent edges. The substance is 
fragile, fracture conchoidal, and very uniform. A mass, Fig. 4., 
which was brought to me by the workman having charge of this 
department, and which he had broken from the end of such a 
stream as I have represented coming from the barrel, presented 
generally the same appearance as a mass broken from an entire 
barrel,j but had this remarkable peculiarity, that there were lines 
—structural lines, a a «a a—whose texture and colour were dif- 
ferent from the general colour of the mass recognisable on such 
points as b b b, between any two such structural lines. 
Fig 2. is an elevation of the stream of pitch, shewing pretty 
nearly the dimensions and outward appearance of the stream. The 
striated slaty structure appears here on the outside, as is more dis- 
tinctly (intended to be) shewn in Fig. 3, ‘There were certain well- 
defined lines, and on either side of these for some little distance, 
other small lines or cracks (but not open cracks or fissures), and then 
a space of smooth glassy-looking pitch. 
I am strongly impressed with the idea, that the structural lines 
are a result of the motion, and that they correspond with the veins 
of glaciers. The lines incline most when the surface is steepest, as 
at h, Fig. 3., and are very faint and nearly horizontal at 7, where 
the surface of the stream is nearly so too. I left Gateshead with- 
out having an opportunity of getting a sectional view of this stream. 
I can get no real Stockholm pitch in Glasgow, else I should have 
made the experiment you have incited me to attempt here. I am, &c. 
Lewis Gorpon. 
Yo Professor FORBES. 
* The numbers refer to drawings sent by Professor Gordon to Pro- 
fessor Forbes. 
+ The pitch is fragile at the same time that it fows.—L.G,. 
