190 THIRTEENTH LETTER ON GLACIERS. [1846. 



13*2 inches daily, or 402 feet annually. The retardation must 

 be attributed to the block having been thrown almost upon the 

 moraine, as happened to the block D 7 under similar circum- 

 stances.* To avoid such a mischance again, I marked the 

 position of a fine block now near the centre of the Mer de 

 Glace opposite to Les Fonts. It was painted with the letter 

 V on both sides, and its position determined with reference to 

 a point on the pathway between the two Fonts, to which it 

 was exactly opposite on the 30th July 1846, when the observa- 

 tions were made. The mark is a cross with the letter V on a 

 small granite block solidly placed on the left of the pathway. 

 The block on the ice is 760 feet distant from the west shore. 



By reference to my Eighth Letter, published in this 

 Journal, and to the fuller details in the London Philosophical 

 Transactions for 1846, on the Plasticity of Glacier Ice, it will 

 be recollected that I made observations at a station marked Q 

 between the Angle and Trelaporte.f This station was 300 feet 

 from the west moraine. The following observations were made 

 last summer in the same part of the glacier, at a distance of 553 

 feet from the moraine : 



Daily Motion. 

 Inches. 



July 23 July 30, 21'5 



July 30 Aug. 3, .... . 20'7 

 Aug. 3 Aug. 14, . . - . . . 21-1 



A very fine block of granite, marked R in oil paint on three 

 sides, about the same distance as Q from the west moraine (300 

 feet), had its position fixed on the 26th August 1844, and was 

 found this year to have moved in 693 days, to 20th July 1846, 

 1108 feet, or at the rate of no less than 19'2 inches daily, or 

 533-6 feet annually, a remarkably rapid motion, but which was 

 carefully verified by two concordant measures. The rate of 

 motion of this block (engaged as it was in the great crevasses 

 near the Angle), from the 23d to the 30th July 1846, was 11 

 feet 4*5 inches, or 20'7 inches daily. 



* See Fifth Letter on Glaciers [p. 36 above.] 

 f [See page 105 above, and the sketch map in Plate III.] 



