Reviews — Professor Jukes' School Manual. 273 



The hornblende of some granites probably contains titanic acid, 

 but its amount in most granites is not large, and in the deposits 

 now specially considered no sign of that mineral is seen. The 

 sphene present in granites is also in relatively very small amount, 

 and its fragments in deposits scarce and irregular in diffusion. 

 Probably all biotite of granites contains titanic acid, if only it were 

 sought for in analysis. We know that in numerous cases rutile is 

 seen in decomposing biotite, though it is apparently by no means 

 a common observation ; and biotites have been proved to contain 

 titanic acid in rocks in which they did not show rutile during 

 decay (e.g. Thiirach, op. cit.). 



That the granitic magma is titaniferous is often proved by the 

 original sphene and rutile present. It seems as if after the separa- 

 tion of these the remainder of the titanic acid were absorbed in the 

 biotite. 



(To be continued in oar next Number.) 



BEVIB W S. 



I. — The School Manual of Geology. By J. Beete Jukes, M.A., 

 F.E.S. Fifth Edition. Edited by A. J. Jukes-Browne, B.A., 

 F.G.S. 8vo. 418 pages ; with numerous Woodcuts. (Black, 

 Edinburgh.) 



alHE late Professor Jukes's motive in preparing this small Manual 

 was to aid young students to get clear notions in both technical 

 and philosophical Geology, and to enable grown-up amateurs to 

 realize " a fair general notion of the scope and nature of that 

 Science." This end and aim has been well kept in mind in all sub- 

 sequent Editions of the book, with conscientious care and creditable 

 results of advanced knowledge in the many divisions of the subject- 

 matter. As it now stands, the School Manual treats of — I. Geological 

 Operations now in action : first, the earth is taken as a whole, with 

 its external features and internal condition ; (2) volcanoes are next 

 considered, and earthquakes, and rise and fall of the ground ; then (3) 

 igneous rocks and their constituent minerals ; (4) rocks mechanically 

 formed, whether on the surface of the Earth by water, ice, and wind, 

 or in the sea, not far from coasts ; (5) rocks of organic origin, 

 whether derived from the accumulation of plants, or of animals. 

 Thus, (1) the destruction and reproduction of strata and other rocks ; 



(2) geological time, as deduced from a consideration of the natural 

 processes and operations, of which these are the results and evidences ; 



(3) the balance of power in the constant action and reaction in the 

 various physical agencies always at work on and in the Earth's crust, 

 are brought clearly before the reader. II. Some of the facts 

 observable in the Crust of the Earth, such as (1) strata or rock- 

 beds, with their lamination and stratification ; (2) rock-blocks, joints, 

 also columnar and spheroidal structure; (3) concretions; (4) inclined 

 and bent strata; (5) faults and lodes; (6) metamorphic rocks; 

 (7) granitic rocks; (8) mountains, hills, and valleys; (9) uncon- 



DECADE III. — VOL. VII. NO. VI. 18 



