Reviews — Geology of Thouars. ■ 419 



are remarkable for their great elongation from north-west to south- 

 east, the innermost being 57 miles long and only 8 miles wide. The 

 central area is covered by thick alluvial deposits, but it lies in the 

 gigantic festoon of the Marri and Bugti Hills, by which the north 

 and south trend of the Baluchistan ranges is interrupted. Mr. Heron 

 considers that the earthquake was probably caused by a movement 

 along a reversed fault, although no trace of deep-seated displacement 

 is visible at the surface. CD. 



REVIEW'S. 



I. — Geology of Thouars. 

 La Geologie des Environs de Thouars (Deux-Sevres) et l'Etage 

 Toakcien. By Professor Jules Welsch, of the University, Poitiers. 

 Mem. Soc. des Sc. Nat. des Deux-Sevres, 1911. 

 rPHE rocks of this district include, as a foundation, Pre-Cambrian 

 1 schists and granitic rocks, and then Toarcian, Bajocian, Bathonian, 

 Callovian, Cenomanian, Turonian, and various Quaternary deposits. 

 Attention is directed especially to the Toarcian of Thouars or Toarcium, 

 where the classic section as seen in the quarries at Yrines shows in 

 downward succession : Plateau deposits (1£ metres), Cenomanian 

 (^ metre), Toarcian (conglomerate and grit, blue marls, ferruginous 

 oolites, yellow marls and limestones, about 10 metres), Pre-Cambrian 

 (schists and slates). 



The Toarcian strata (as originally grouped by d'Orbigny) are 

 divided into the following zones or palseontological horizons by 

 Professor Welsch : — 



Ammonites opalinus (with Rhynchonella cynocephala, Terebratula 



infra-oolithica, etc.). 

 A. aalensis (with Dumortieria Moorei, etc.). 

 A. radians (with Catulloceras dumortieri, etc.). 

 A. insignis (with Grammoceras fallaciosum, etc.). 

 A. toarcencis (with G. cf. striatulum, etc.). 

 A. variabilis (with Lytoceras sublineatum, etc.). 

 A. bifrons (with Dactyloceras holandrei, etc.). 

 A. falcifer (with D. annulatum, etc.). 

 The conglomerate and grit (1 to 3 metres thick) which rests 

 irregularly on the Pre-Cambrian was at one time grouped with the 

 Middle Lias, but Professor Welsch, after prolonged research, found in 

 the strata an ammonite near to Harpoceras Strangewaysi, and he 

 groups the beds with overlying layers in the zone of Ammonites 

 falcifer. 



He remarks that there is a gradual passage from one zone to 

 another in the Toarcian of Thouars, and that the type of the stage has 

 been well chosen in the quarries of Vrines-Thouars, where there occur 

 neither the Ammonites of the Middle Lias nor those of the Bajocian. 



After commenting on the Aalenian division of Mayer - Eymar, 

 Professor Welsch observes that there are affinities between the beds 

 with Lioceras opalinum and those with Ludwigia Miirchisonce, while 

 again it is difficult to separate the higher zonal stages in the Bajocian, 

 the divisions being arbitrary and local. 



