278 Revieics — ITarJier's Students' Petrology. 



The outcrops of the Tertiary strata are not indicated on the map, 

 but the entire area is coloured according to the distribution of what 

 "would ordinarily be termed the main subsoils. Thus there are areas 

 of many square miles coloured simply as Miami sandy loam. The 

 surface soil is stated to comprise up to 15 inches " of brown sandy 

 loam of medium texture, containing a good proportion of fine gravel. 

 The subsoil, to a depth of 36 inches or more, consists of a yellow or 

 gray light sandy loam or sand, containing fine gravel. From 5 to 10 

 per cent, of larger gravel and glacial cobbles is scattered through both 

 soil and subsoil, and occasional glacial erratics of larger size are 

 found. Irregular bands of gravel are found here and there at different 

 depths throughout the type." 



Again, the Galveston coarse sand " consists of 3 feet or more of 

 medium to coarse loose gray sand, containing gravel of various 

 sizes." The Much "consists of vegetable mold in a more or less 

 decomposed condition, mixed with silt or other earth, and extending 

 to a depth of from 1 to 3 or more feet." 



The value of soil surveys so far as the maps are concerned is 

 in the indication they give of the main characters of the subsoil, 

 or weathered geological formation beneath the soil. Added to this 

 information, that relating to the actual depths of soil and subsoil, 

 obtained by means of hand-borers or spade, and the mechanical and 

 chemical analyses of the materials, combine to give data of great 

 practical value. 



YII. — Petrology for Students : Ak Introduction to the Study of 

 Rocks under the Microscope. By Alfred Harker, M.A., E.Il.S. 

 Foui'th edition, pp. viii, 336, with 91 text-illustrations. Cam- 

 bridge : at the University Press, 1908. 

 ANEW edition of this eminently concise and useful handbook will 

 be welcomed not only by students of petrology, but by geologists 

 in general, enabling them, as it does, to keep in touch with the 

 progress of the science and the nomenclature of the rocks. 



It is remarkable that the author has revised and brought his book 

 up to date not only without increasing its size, but by a reduction of 

 ten pages compared with the last edition. 



Since then Mr. Harker has published the results of his researches 

 on the Tertiary Igneous Rocks of Skj^e (Mem. Geol. Survey, 1904) 

 and of other investigations among the Inner Hebrides. Thus we find 

 brief reference to his " Mugeary type " of olivine-dolerite, recorded as 

 mugearite in the index, though the author has purposely refrained 

 from using the rock-name in the text. Other varieties of rock are 

 similarly treated, such as the olivine monzonite (Kentallen type) and 

 a connecting link between syenites proper and nepheline-syenites 

 (Pulaski type), which are recorded only in the index as kentallenite 

 (Hill and Kynaston) and pulaskite (J. F. Williams). The value of 

 the index is enhanced by the insertion of the names of the authors 

 responsible for the rock-terms. 



The descriptions of the sedimentary rocks and of the effects 

 produced by metamorphism are amplified by references to the more 

 important publications on these subjects. 



