Geology and Natural History. 161 



the experimental mechanics of geology, and the facts tend largely 

 to confirm previous views regarding the origin of laccoliths, 

 especially in respect to the importance of viscosity of the magma 

 as a factor in their production. l. v. p. 



3. Analcite in Igneous Rocks. — In a recent paper on a mon- 

 chiquite from Mount Girnar Junagarh, Kathiawar (Quar. Jour. 

 Geol. Soc, vol. lvii, p. 38, 1901), Dr. J. W. Evans shows that 

 the isotropic base is composed of analcite. This is proved by 

 its chemical composition, specific gravity, optical properties and 

 reaction with acids. The author remarks that it might have all 

 these characters and still be a structureless glass. This is true, 

 but only as a possibility so remote that it may be said to have 

 little practical importance. When we consider that a glass has 

 no definite composition, and that to satisfy the properties 

 demanded by analcite there must be five numerical factors 

 (including sp. gr.) which must be arranged in definite ratios, the 

 great improbability of such an agreement becomes at once evi- 

 dent. Adding to this agreement the capability of gelatinization, 

 possessed by basic glasses, but so far as known not by silico- 

 aluminous ones, and still more the improbability of glass forming 

 under such physical conditions as have influenced the crystalliza- 

 tion of these dikes and the probability becomes still more remote. 



But Dr. Evans has called attention to still another means of 

 discrimination, the cubic cleavage of analcite. This is quite 

 marked in the rock from India and is clearly shown in the micro- 

 photograph of the thin section. The suggestion of the use of 

 this character, overlooked by previous investigators, is a valu- 

 able one where it can be applied. I have studied a section from 

 the original type of Rosenbusch, from the Santa Cruz Railway 

 near Rio Janeiro, and under high powers the cubic cleavage of 

 the analcite is very clear and evident, thus confirming its crys- 

 talline nature. A study of similar rocks from other localities 

 shows in some cases this cleavage in the isotropic base, in other 

 cases it is apparently wanting. Where the areas of the base are 

 comparatively large it usually appears, where the amount of base 

 is very small and the interspaces minute it cannot be detected. 

 Often, however, in these cases the base by a more reflected light 

 is seen to be of fine granular or even fibrous character, thus indi- 

 cating crystallization of some sort. l. v. p. 



4. Researches on Cellulose, 1895-1900 • by C. F. Cross and 

 E. J. Bevax. London, 1901 (Longmans, Green & Co.). — A 

 previous volume by these authors, in 1895, gave a comprehen- 

 sive view of the subject of cellulose, up to that date. It con- 

 tained, also, a full account of the interesting discovery made by 

 them, that cellulose treated with caustic alkali dissolves in carbon 

 disulphide, and can be recovered from this solution in a more or 

 less pure state. The authors also described to some extent a 

 technical product obtained by them, on carrying out this process 

 with certain modifications of detail. This product, now known 



Am. Jour. Sci. — Fourth Series, Yol. XIII, No. 74.— February. 1902. 

 11 



