Geology and Natural History. 341 



miles below the surface will have allowed the injection of the 

 lower rocks amongst the upper ones, and the phenomena which 

 we should expect to find according to Mr. Davison's theory are 

 eminently in accordance with observation. It therefore appears 

 to me that his view has a strong claim to acceptance." 



2. Lavas of Mrakatoa. — Prof. Judd reviews the analyses of 

 these lavas (Geol. Mag., vol. i, 1888), and shows that they are es- 

 sentially andesyte, in which enstatite predominates over the py- 

 roxene, and that much glass is present. Yet they vary greatly 

 in the proportions of the constituent minerals and hence widely 

 in ultimate composition. There is a large difference also in the 

 condition of the glassy base as to its microlites, their number, 

 grouping, and other peculiarities. A fragment of the obsidian, 

 on approaching a white heat, swells up as it melts into a cauli- 

 flower-like mass five or six times the size of the original, proving 

 the presence of some volatile material which is given off at a 

 high temperature. The amount of distension undergone was 

 found to be 3-J to 7, 8 or even 9 times that of the glass. The ob- 

 sidian sometimes contains knots of pitchstone, the feldspar crys- 

 tals of which show the effects of a large amount of corrosion, 

 and sometimes of re-solution. Dr. Judd observes also that the 

 stony lavas sometimes have the feldspar, pyroxenes and magne- 

 tite aggregated in little knots, producing a kind of structure 

 which he calls glomero-porphyritic. 



3. Geologie von Bay em, von Dr. K. Willhelm von Gumbel. 

 First Part, Elements of Geology. Lieferung 5, in continuation 

 of volume I, pp. 961 to 1088 8vo, with numerous illustrations. — 

 Although entitled Geology of Bavaria, this work by Dr. von 

 Gumbel so far as published is essentially a comprehensive treatise 

 on the science. The sheets here issued treat of the Pliocene, 

 Quaternary, and Recent periods, and then commences, on p. 1020, 

 a new division of the work, on Geogeny or the development of 

 the Earth. 



4. Recent contributions to our knowledge of the vegetable cell. — 

 Die Morphologie und Physiologie der Pflanzenzelle, von Dr. A. 

 Zimmermann. 8vo, 223 pp. (From Schenk's Handbuch der 

 Botanik.) Die morphologische und chemisette Zusammensetzung 

 des Protoplasmas, von Dr. F. Schwarz. 1887. 8vo, 244 pp. 

 (In Cohn's Beitrage zur Biologie der Pflanzen. Bd. V.) Articles 

 in current Journals, cited in the text. 



The progress which modern methods of research have permitted 

 Vegetable Physiology to make is shown by even a superficial 

 comparison of the classical treatises of Mohl (1851) and Hof- 

 meister (1867) with any of the recent publications on the same 

 subject, for example, with that placed at the head of the list 

 given above. It will be remembered that Mohl described pro- 

 toplasm and first gave it its name in 1846, and therefore, at the 

 time of the publication of his "Vegetable Cell," his attention was 

 directed largely to the examination of the cell-contents; whereas, 

 up to that time, a great part of the study in this field had been 



