Reviews — Pe7ining^s Field Geology, 467 



indications of metamorpliism ; while the remarks quoted from Lyell 

 (p. 120) can scarcely be said to represent the present state of our 

 knowledge of metamorphic rocks. 



The advice furnished on the construction of Horizontal Sections 

 on the use of the Aneroid, the Level, and the Theodolite, is very 

 good, and the author rightly points out the necessity of obtaining a 

 true outline of the ground. 



In very complicated districts Jukes's plan of inserting only the 

 facts observed might be more generally adopted with advantage ; 

 and in all cases it is well to distinguish between actual sections and 

 purely diagrammatic sections. 



The remarks on Lithology and the tables for the determination of 

 rocks and minerals cannot fail to be useful. 



Mr. Jukes-Browne gives a good account of the character and mode 

 of occurrence of fossil remains, with hints for collecting. The 

 necessity, unfortunately too little attended to, of keeping accurate 

 records of stratum and locality is insisted upon. The practice also 

 of only keeping '' typical specimens " is justly condemned, since, 

 as the writer remarks, '' it tends to confirm the old superstition 

 that species are definite abstractions, and to draw hard and fast 

 lines between cognate forms which are unnatural and non-existent 

 in reality." 



The value of palseontological evidence is fairly treated, and the 

 impolrtance of their stratigraphical position being well established 

 before they are used as a clue to the identification of isolated deposits, 

 is likewise noted. 



Mr. Penning has carefully compiled a list of characteristic fossils 

 arranged alphabetically under each zoological order, so that if a 

 species of fossil be known, the approximate (if not exact) geological 

 position of the rock to which it belongs can readily be determined. 



We have said little about the method of drawing boundary-lines, 

 as we can confidently recommend the Guide before us. Those who 

 start with this book as a companion will soon be able to grasp the 

 method of tracking the divisional line between two formations, but 

 it would be difficult to draw hard and fast rules, inasmuch as the 

 character of the work and the evidence to be relied on varies much 

 with the different rocks. The irregular cappings of Drift gravels 

 and Boulder-clay, the tolerably regular escarpments of the Secondary 

 and Upper Palgeozoio rocks, and the often confused state of tlie 

 Lower Palseozoic rocks, involve distinct kinds of evidence and trains 

 of thought. 



But in all cases such evidence as that furnished by springs, soils, 

 and the form of the ground, must receive its due attention ; and in 

 all cases the results of ancient and modern landslips must not be 

 neglected. 



That the work might be amplified with advantage the author 

 himself admits, and in the event of a second edition we should like 

 to see a chapter intended for those who set to work in an entirely 

 fresh country where little or no order in the succession of rocks has 

 been made out. 



