Correspondence — Professor Prcdunch, D.C.L. 237 



of these sh'uctures that an explanation of the phenomena can be 

 found. I quite admit that some of Mr. Watts's sections showed 

 that the perlitic shrinkage fissures of the g]ass-magma did pass into, 

 and through, the quartz-crystals ; but it is not to be inferred from 

 this that the quartz-crystals had perlitic structure, as I shall 

 endeavour to show. Let us consider for a moment the process of 

 consolidation from the molten state. It is clear that the silica 

 consolidated before the glass-magma ; and in forming distinct 

 crystals it obeyed the law of its molecular constitution, which 

 obliges it to take the form of a hexagonal prism terminated by a 

 pyramid. On the other hand the amorphous (or non -crystalline) 

 magma is governed by an entirely different set of molecular forces 

 and tries to form a series of concentric globules, somewhat as basalt 

 on cooling often forms globular masses with concentric envelopes. 

 The globular is the primary form of a cooling body. It is 

 clear that the molecular constitutions of the quartz-crystal and 

 of the non-crystalline magma are essentially different, and this 

 distinction finds its result in the diverse forms and structures of 

 the two. If this be admitted it will not be difficult to account for 

 the apparent perlitic fissures traversing some of the quartz-crystals, 

 as shown in some of the specimens. Though these have had priority 

 over the magma in consolidation, yet they were necessarily highly 

 heated and somewhat soft owing to the liquid state of the enclosing 

 magma; and this being so, as the perlitic fissures were being 

 developed in the latter they would exert a pull upon the parts of 

 the quartz-crystals in contact, the force developed by contraction in 

 the case of each globule of the magma tending to draw the mass 

 towards its centre. The quartz being (as has been observed) in a 

 somewhat soft condition would be unable to withstand this force, 

 and in such cases it would give way ; and fissures would be 

 produced continuous with one or more in the enclosing glass- 

 magma ; bnt this does not prove that the quartz itself has a perlitic 

 structure. Edward Hull. 



22nd March, 1894. 



ON THE POSSIBLE MAEINE ORIGIN OF THE LOESS. 

 Sir, — One of the difficulties that faced me in my paper on the 

 " Submergence of Western Europe " ^ was the want of evidence to 

 prove distinctly that the land had been under the sea. As, however, 

 all the physical evidence concurred to show that the various forms 

 of the Rubble-drift indicated a transient disturbance, I concluded 

 that the submergence had been of too short a duration to allow of 

 the establishment of a marine fauna in the area submerged. It was 

 therefore with much satisfaction that I found the other day con- 

 firmation of a very unexpected character in a paper published in the 

 last number of the " Bulletin de la Societe Beige de Geologic."^ In 

 treating of the Loess I described a portion of it as of fluviatile origin, 



^ PhiL Trans, for 1893, p. 903. 

 2 Ibid. March 1894, p. 118. 



