llcmarls on Glacier T/icories. 337 



which is possible for the texture. If in any part liie texture 

 gives way, we shall have fissures nearly perpendicular to the 

 transv(?i-se curves. On this supposition of a flexible "lacier, we 

 have (1) original transverse straight lines drawn into curves of 

 limited Jlc'xiire ; (2) the substance in a state of distortion, from 

 which hand specimens would instantly recover; (3) a homoge- 

 neous texture of such specimens." Again, it is stated that, on 

 the supposition of the glacier being viscous or plastic, filaments 

 will slide past each other in lines directed towards the middle, 

 and that the mass will thus be separated according to such 

 lines. Also, " if the texture of the substance yield to the ten- 

 sion which tends to separate it directly, we shall have fissures 

 in directions perpendicular to the directions just described" 

 (those in which the particles slide past each other). It is then 

 stated, that we should have "(I) original transverse straight 

 lines drawn into curves of Mw/mzVe-rf flexure ; (2) the texture 

 of the substance in a state of equilibrium, so that hand speci- 

 mens have no distortion to recover from ; (3) a handed texture, 

 the bands being traces of parallel fissures." 



It will be seen at once that these statements, made as though 

 they contained only recognised facts or incontrovertible con- 

 clusions, do really contain most of the controverted points in 

 the subject. In the first place it is stated, on the supposition of 

 glacial ice \i^\x\^jiexible^ that fissures would be formed nearly 

 perpendicular to the transverse curves above mentioned. In 

 my Second Letter (arts. 4, 7, and 8, p. ll'S, &c.) I have given 

 three different proofs that such will not be the case. 1 can 

 only challenge the refutation of any one of them. It is rightly 

 asserted that, previous to fracture, the curves would be oi li 

 mitedjlexure ; but it is not correct that hand specimens would 

 instantly recover from their state of distortion, for that would 

 require the mass to be perfectly elastic^ a property which it 

 would be absurd to attribute to it. The assertion (3) that 

 the texture would be homogeneous^ involves the hypothesis thai 

 the banded structure can only arise from the formation of 

 planes of discontinuity, applying the assertion to an actual 

 glacier. But this is one of the points at issue, not to be settled 

 assuredly by the mere assertion of any one. Is your corre- 

 spondent acquainted with all the mysteries of crystallization*? 



* I may here mention a curious effect of crystallization in the structure 

 of hailstones, which proves beyond doubt that the alternations of opake 

 and transparent ice may result from it. In the desolating hailstorm which 

 passed over Cambridge on the 9th of August 1843, many of the hailstones 

 were of the form of rather flat double convex lenses, nearly as large as the 

 palm of the hand, and consisted of white opake ice in the centre, sur- 

 rounded by a ring of dark transparent ice, with an exterior ring of ice like 

 that in the centre. In some cases there were several dark rings, the ceii- 



Phil. Mag. S. 3. Vol. 26. No. 173. April \M5. 2 A 



