512 RevieiDs — Tate 8^ Blahe — On the Yorkshire Lias. 



lledcar to the shores of the Humber with several inlying tracts, but 

 apparently no outliers. The authors have carefully traced out the 

 boundaries of its three divisions, Upper, Middle, and Lower Lias ; 

 and these are coloured on a map drawn to the scale of half-an-inch 

 to a mile, which accompanies their volume. The Ehsetic beds are 

 so feebly developed that they have not been able to separate them 

 from the Lower Lias on the map. 



The first part of the work commences with a general account of 

 the range of the Liassic strata on the Continent and British Isles. 

 Notices of the literature of the Yorkshire Lias are given, and its 

 range, extent, and general characters are then pointed out. The 

 relations with the Inferior Oolite are also discussed. 



One chapter is devoted to an Historical Sketch of the Discovery 

 and Industrial Applications of the Cleveland Main Seam ; the beds 

 of Jet and Jet-working receive due attention, as likewise do the 

 faults and the basaltic dyke. The bulk of Part I. is, however, taken 

 up with the minute account of the strata and their fossils, of which 

 latter a sjmoptical table is given. 



The zones described in the Lower Lias are those of Ammonites 

 planorhis, A. angulatus, A. Bucklandi, and A. oxynotus. 



Oppel's zone of A. Turneri is included in that of A. BucMandi, 

 because the species associated with it are common forms in the latter 

 zone. Nor do the authors find suf&cient palseontological reasons for 

 adopting the zones of A. obtusus and A. raricostatus, the latter in- 

 cluding part at least of what they call the region of A. armatus, and 

 include in the Middle Lias. 



In the Middle Lias they recognize the zones of A. Jamesoni, A. 

 capricornus, A. magaritatus, and A. spinatus, but include Oppel's zone 

 of A. Ibex with that of A. Jamesoni. The Upper Lias is described 

 under the zones of A. annulatiis, A. serpentinus, and A. communis. 

 The junction-beds with the Inferior Oolite are described as the zone 

 of A. Jurensis, and from these they exclude the Blea-Wyke (some- 

 times called Blue Wick) beds. 



In their concluding chapter the authors draw attention to the 

 nature and origin of the Yorkshire Lias. No portion of the beds 

 was in their opinion deposited in very deep water, but they find 

 two distinct areas possessing distinct features, and which separation, 

 begun in early Liassic times, appears to have continued throughout 

 the Jurassic epoch, being exemplified by the characters of the Lower 

 Oolites, and the development of Corallian and Portlandian strata. 



In lithological characters the Lias is very variable, and yet its 

 gi'eat thickness, and complete representation of every portion in one 

 form or another, make the Yorkshire series a better exemplification of 

 the whole deposits of the. period than can be found in any other 

 locality. The great feature, as they remark, is the pal£eontology, and 

 the determination of those zones of life which puzzle the naturalist 

 and sometimes raise the scepticism of the field-geologist. The cause 

 of these life-zones they cannot explain. The change of Ammonite- 

 forms is not due to the surrounding physical agencies that are 

 observable, but to some others which have left no indication of their 



