confirming the Viscous Theory of Glaciers. 207 



nor have I had any report of the progress of my pitch glacier 

 since the 6th of January, when I was informed it had not 

 moved since the day after I left it on the 28th of 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 ; 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 ' dirt-bands ' on the surface. I was let down into 

 several crevasses, one of them to a depth of thirty feet, and 

 could trace the daty structure of the ice ; the alternate clear 

 blue thin veins, and the transition to opake gray, or even 

 white. I descended from the glacier with a much better ap- 

 preciation 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 appearance is re- 

 presented in Plate I. fig. 1. 



"A mass of Stockholm pitch broken from a barrel in August 

 (at the time of the observations I am about to mention) pre- 

 sented a dark brown colour, a glassy lustre, translucent edges. 

 The substance is fragile, fracture conchoidal and very uni- 

 form. A mass (fig. 4) which was brought to me by the work- 

 man 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 appear- 

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

 remarkable peculiarity, that there were lines, — structural lines, 

 a, or, a, a, whose texture and colour were different from the 

 general colour of the mass recognizable on such points as h,b, h, 

 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 (intended 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 ope7i cracks 

 or fissures), and then a space of smooth glassy-looking pitch. 



" I am strongly impressed with the idea that the structural 

 * The pitch h fragile at the same time that it flows. — L. G. 



