270 APPENDIX, NO. IV. 



<t 



" Allow me in the first place to mention that I read your Travels 

 in the Alps in May last ; that on the 24th of June I spent almost 

 twenty hours on the glaciers of the Grindelwald. I went up by the 

 lower glacier prepared with poles to prove its motion, and actually 

 observed a progress of above twelve inches in the course of thirteen 

 hours, from 6 A.M. to 7 P.M. I traced the l dirt-bands ' on the sur- 

 face. I was let down into several crevasses, one of them to a depth 

 of thirty feet, and could trace the slaty structure of the ice ; the alter- 

 nate clear blue thin veins, and the transition to opaque gray, 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.* 



" A mass of Stockholm pitch broken from a [the] 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 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 repre- 

 sented coming from the barrel, presented generally the same appear- 

 ance as a mass broken from an entire barrel, f but had this remarkable 

 peculiarity, that there were lines structural lines, whose texture and 

 colour were different from the general colour of the mass recognizable 

 on points between any two such structural lines. 



" Fig. 2 is an elevation of the stream of pitch, showing pretty nearly 

 the dimensions and outward appearance of the stream. The striated 

 slaty structure appears here on the outside, as is more distinctly (in- 

 tended to be) shown 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, and are 



* [The reference to the figures is here omitted. The figures will be found in 

 the volume of the Philosophical Magazine referred to.] 



f " The pitch is fragile at the same time that it flows." L. G. 



