134 Reviews — The Jurassic Rods of England. 



leading fossils of each, some of them being taken to indicate subzoncs, 

 being mentioned. Owing to the earlier incoming of " Portlandian 

 conditions" in some parts of the Continent, we consider that the beds 

 so identified are partially homotaxial rather than synchronous; this 

 is particularly well seen in the case of certain Trigonia and other 

 characteristic shells of the more estuarine beds. The zone of 

 Am. gigas in this country is a conventional one, and if we must 

 have an Ammonite to represent the Astarte Samanui-heds of 

 Swindon, Am. pectinatus would seem more appropriate. 



The local details of the Portland beds vary greatly in the several 

 districts; yet, notwithstanding certain differences in lateral develop- 

 ment, these beds have been correlated by Prof. Make. The building 

 stones are not always on the same horizon ; the main building 

 stones of the Vale of Wardour, for instance, occupying a lower 

 position than those of the Isle of Portland. The Isle of Purbeclc 

 presents us with the most massive development of Portland rocks, 

 but they are less interesting from a palasontological point of view 

 than those of Portland Isle and the Vale of Wardour, whilst the 

 Upper Portland beds of Swindon are quite abnormal in their de- 

 velopment. Again, a very distinct type of beds, smaller in volume 

 but often richly fossiliferous, occurs in Buckinghamshire. It has 

 always seemed to us that there are evidences of considerable wasting 

 of Portland beds, very noticeable in the Isle of Purbeck and in the 

 Vale of Wardour, before the Purbeck strata were laid down : these 

 evidences Mr. Woodward seems inclined to minimize. 



Purbeclc Beds (Piirbeclcian). — These attracted the notice of 

 geologists at an early period, so that there is a considerable literature 

 on the subject. The present volume supplies us with a useful 

 summary, besides including many details now for the first time 

 published. The author, no doubt, rejoices that at length he is free 

 from the necessity of recognizing Ammonite-zones, though, as he 

 remarks, "our Purbeck strata may be equivalent to beds on the 

 Continent . with a marine fauna and grouped in the zone of 

 Am. transitorius." In the Alpine region we may regard them 

 as corresponding in the main with the Upper Tithonian, whilst in 

 the north-east of England "they may be in part equivalent to the 

 zone of Belemnites lateralis of the Spilsby Sandstone and Speetou 

 beds." This latter correlation was indicated by Pavlow, and seems 

 a very reasonable supposition. 



The chief points of a controversial character in connection with 

 the Purbecks are: (1) the exact nature of their relationship to the 

 underlying Portlands, and (2) where to draw the line between 

 Jurassic and Cretaceous in the great fresh-water series, which, in 

 this country, occupies an episodal interval between the marine beds 

 ot these two great systems. On this latter point the correlation of 

 the Purbeck beds of the English Channel with those of Other 

 localities opens up some interesting questions. This is especially 

 the case as regards the Vale of Wardour, where Messrs. Woodward 

 and Strahan demur to the conclusions of Messrs. Andrews and Jukes- 

 Browne to the effect that strata hitherto regarded as Wealdeu should 

 be classed with the Upper Purbeck. 







