422 Reviews — 3IM. A. Pavloiv and C. W. Lamplugh — 



breadth. It is clear that the wave the book now forms must be regarded as made 

 up of three sections : viz. a section forming the outside of the trough on the one 

 side, and a section forming the outside of the arch on the other, and a central or 

 common section, which may be regarded either as uniting or dividing the other two. 

 As this experiment gives us a fair representation of what takes place in a 

 geological fold, we see at a glance that the geologist is forced to divide his fold into 

 three parts — an arch limb, a trough limb, and a middle limb — which latter we may 

 call the copula or the septiim, according as we regard it as connecting or dividing 

 the other two. Our note-book experiment, therefore, shows us also that in the 

 trough limb and the arch limb the leaves or layers undergo scarcely any change of 

 relative position beyond taking on the growing curvature of the wave. But the 

 layers in the central part, or septum, undergo sliding and shearing. It will be 

 found also, by gripping the unbound parts of the book firmly and practicing the 

 folding in different ways, that this septum is also a region of warping and twisting. 

 This simple experiment should be practised again and again until these points are 

 apparent, and the various stages of the folding process become clear ; the surface of 

 the book being forced first into a gentle arch-like rise with a corresponding trough- 

 like fall, then stage by stage the arch should be pushed over on to the trough until 

 the surfaces of the two are in contact and the book can be folded no further. 



(To he continued!) 



IR E "V I S "VvT S. 



L — Argtlbs de Speeton et leurs Equivalents. By A. Pavlow 

 and G. W. Lamplugh. Extracted from the " Bulletin de la 

 Societe Iinper, des Naturalistes de Moscou," Nos. 3 and 4, 1891. 

 With eleven plates (Moscow, 1892). 



THAT the study of life-zones furnishes the key to the elucidation 

 of the relationship of fossiliferous rocks, however widely 

 separated geographically, has long been recognised by palaeontolo- 

 gists, and this lesson is enforced anew in the admirable monograph 

 before us. 



The aiathors divide their work into three parts ; the first (pp. 

 1-33) contains a description of the beds at Speeton (Speeton Clay) 

 and their equivalents in Lincolnshire, by Mr. Lamplugh ; the second 

 (pp. 34-155) gives a description, written by M. Pavlow, of those 

 forms of Mesozoic Cephalopods — Belemnites and Ammonites — 

 which are of the greatest importance for purposes of comparative 

 stratigraphy. These fossils are compared with the fossils of other 

 countries, chiefly with Eussian forms, of which some are figured as 

 well as described. This part of the work is preceded by a table 

 (pp. 36-37) indicating the sub-divisions of the Jurassic and Lower 

 Cretaceous beds of the neighbourhood of Moscow, and of the lower 

 Yolga region (Bas Wolga). Furthermore, M. Pavlow deals with 

 the relationship between the Speeton and Lincolnshire beds and 

 those of other countries (pp. 156-201). 



The material upon which the memoir under review was based 

 consisted in the main of Mr. Lamplugh's collection of fossils made 

 at Speeton and in Lincolnshire, supplemented by many specimens 

 lent to the authors by the officials connected with some of the 

 leading Continental and British Museums. 



In order to make clear the remarks which follow we here repro- 

 duce part of a stratigraphical table furnished by M. Pavlow, showing 

 the different " zones " into which the Speeton and Eussian beds 

 have been divided. 



