82 Revieivs — R. S. Tarr — College Physiography. 



existence in Arkansas 1 and elsewhere of pisolitic laterites formed 

 entirely of aluminium hydrate with three molecules of water, largely 

 in the colloidal state, and only crystallized in cracks, shows that if 

 this cause can be admitted in certain cases, it is not the general rule. 

 The Hardening of Laterites. — This is regarded as a non-essential 

 property of laterite, due to the evaporation on exposure to the air of 

 the quarry water contained in the colloidal hydroxides and silicates, 

 and particularly in the hydroxide of iron. 2 It is only seen in those 

 laterites containing these products in abundance, and is absent from 

 the gibbsitic laterites derived from the diabases and syenites. 



(To be concluded in the March Number.) 



EEVIEWS. 



I. — College Physiography. By R. S. Take; edited by L. Martin. 

 pp. xxii -f- 836, with 10 coloured maps and 503 text-figures. 

 New York: Macmillan, 1914. Price 15s. 



f PHE late Professor R. S. Tarr was well known in this country as 

 | one of the ablest exponents of the modern American school of 

 physical geography. Besides publishing during his lifetime several 

 small textbooks of physiography, he projected a large and compre- 

 hensive work on the same subject. At the time of his death in 1912 

 some twenty chapters of the book were written ; after consultation 

 with Mrs. Tarr and some leading American geographers, Professor 

 Lawrence Martin, of the University of Wisconsin, undertook to supply 

 the remaining chapters and to edit the whole work. The result is 

 a book of over 800 pages, with some 500 illustrations. As stated in 

 the editor's preface, it is intended "for use in elementary physical 

 geography courses in universities, colleges, and normal schools, for 

 supplementary reference-reading by high-school students who are 

 using a more elementary text, and for general reading by laymen of 

 mature years ". The first reflection that suggested itself to the 

 reviewer is that American college students cannot be in the habit of 

 doing their serious reading in arm-chairs, such a proceeding in this 

 instance being barred by the enormous weight of the book, which 

 scales nearly 4 lb. avoirdupois. 



change in the state of hydration of the oxides of aluminium and iron once they 

 have been deposited, except in the cuirass, where the limonite and stilpno- 

 siderite tend to lose their water with formation of hematite, whilst the 

 aluminium hydrates are unaffected. 



1 Lacroix was able to visit the bauxite deposits near Little Bock last summer, 

 and concludes that they must be regarded as laterites formed from alkaline- 

 syenites, with kaolin characterizing the zone of leaching and bauxite the zone 

 of concretion. 



2 It is interesting to recall here Holland's suggestion that the loss of water 

 accompanying the hardening of laterite is due to the crystalline affinity of 

 Fe 2 03 in two molecules of limonite leading to the formation of crystalline 

 hematite with rej ection of water. 



