Reviews — 2'h.e Channel Islands. 41 



plainly signifies that the water in turgite is held in a different way 

 from that in the other hydrated oxides ", and later, " no sudden 

 decomposition takes place anywhere, and it would seem that turgite 

 unlike the other hydrated ferric oxides, is not a definitely hydrated 

 compound." How are these statements to be reconciled with the 

 view that some turgites contain about 50 pev cent of goethite ? 

 Of many other points of interest the following may be chosen : — 



(a) The orange to orange-yellow hydrates (Class I) are found to 

 begin to decompose at an apj^reciable rate at about 200° C, while 

 at about 300° C. their decomposition becomes labile. 



(b) For the same class, dehydration is irreversible where combined 

 water is concerned, and approximately reversible where uncombined 

 water is concerned. 



(c) For turgite (Class II) dehydration is irreversible, but no 

 temperatures comparable with those referred to in (a) have been 

 detected. 



In conclusion one may perhaps venture on a complaint. Much 

 might have been gained by clearer exposition. It will suffice to 

 mention a couple of instances of unnecessary obscurity in regard 

 to figure 2 with its fourteen independent graphs. Each graph is 

 numbered, and the reader is referred to two tables elsewhere in the 

 paioer to find, by help of these numbers, under what names the 

 fourteen specimens experimented with were received from various 

 museums. It is a matter of further research to realize how far 

 this naming has been accepted by the authors. It would have been 

 a great help to have had the author's naming indicated by initials 

 in the corner of each graph, as, for instance, Li. for limonite. Then 

 again, figure 2 is described as giving " temperature — time dehydra- 

 tion curves ". It appears that each graph in the figure co-ordinates 

 successive temperatures of a hydrate charge with the differences 

 of these temperatures and those of a control body, where both 

 charge and control have been heated in a furnace regulated to raise 

 the control's temperature at a roughly uniform rate. But to make 

 certain of all this one has to turn to previous literature. 



E. B. Bailey. 



I 



The Channel Islands. By John Parkinson. Handhuch der 

 regionalen Geologic, vol. iii, pt. i, pp. 335-41. Heidelberg, 

 1916. 

 N Steinmann's Handhuch der regionalen Geologic, Mr. John 

 Parkinson gives a clear outline of the Geology of the Channel 

 Islands, a subject to which he made formerly some valuable contri- 

 butions. It is illustrated by geological sections and small maps of 

 the principal islands. In Jersey the oldest sedimentary rocks are 

 probably Brioverian, and in them are some contemporary volcanic 

 rocks, ending with the remarkable rhyolites of BoulayBay and Anne 

 Port. Intrusive granites and diorites also occur, the latter being the 



