586 



J. F. BLAKE ON THE TJPPEE 



here less distinct than elsewhere ; for if Coquand is right in recording 

 Cardium dissimile from the latter, and the shell called Astarte 

 rugosa has been rightly determined from Chassors, there is a very 

 Portlandian aspect even about the Lower Limestone, though it would 

 be impossible, for stratigraphical reasons and from the general cha- 

 racter of its fauna, to separate it from the Upper Bolonian. Thus 

 there is nothing to absolutely prevent a geologist from considering, 

 with Coquand (24), that the gypseous beds at the top belong to the 

 Upper Portland, i.\e. Purbeck ; but it is more in keeping with proba- 

 bility to regard them as taking the place, without any intervening 

 gap, of the Lower Portland or true Portland limestone, as Manes 

 does (17) when he groups the equivalent beds in the He d'Oleron 

 with those below. In the latter locality, at St. Denis, it is undoubted 

 that beds with Cardium dissimile follow very closely on others with 

 Cyprina Brongniarti (or its representative) ; and these we are justified 

 in considering Portlandian. They are followed conformably by the 

 gypseous beds, which are associated with others containing fossils 

 like the beds below ; and these too, therefore, are placed as Lower 

 Portlandian. In. the Pays de Bray it has been satisfactorily shown 

 that above the Upper Bolonian clays come ferruginous grits contain- 

 ing true Trigonia gibbosa ; and these are therefore rightly placed 

 by de Lapparent (69) and Ssernann on the horizon of the Lower Port- 

 landian of the present paper. In the Boulonnais the beds hitherto 

 called " Upper Portland " correspond without doubt to the true 

 Portland limestone, but not to the whole of it. Throughout they 

 are more or less arenaceous, and correspond lithologically to the 

 Flinty series, while their characteristic Ammonite is A. bononiensis, 

 and not A. giganteus, which latter is characteristic of the Building- 

 stones. Here, therefore, the Portland series is incomplete ; and the 

 beds which lie at the top and contain Astarte socialis and Cyprids 

 are, for this reason, scarcely likely to represent Purbeck beds. They 

 are in fact so rubbly and irregular that they cannot be considered 

 conformable, and may be of any age, either Purbeck or Wealden ; 

 but there is not the slightest proof that they belong to the former. 

 Finally, in our own country it has been shown (Q. J. Gr. S. vol. 



xxxvi. ) that the Portland limestone is only complete in Dorsetshire 

 and the Vale of Wardour ; and in these two districts the freshwater 

 (or partially freshwater) strata will belong to the Upper Portlandian, 

 and be its only representatives. Justifications for a closer associa- 

 tion of these rocks with the Portland marine limestones than is 

 allowed by calling them Purbeck, may be found in the occurrence 

 in them of Hemiddaris purbeckensis in Dorsetshire, a fossil found 

 also in the Upper Bolonian, and of Trigonia densinoda, belonging 

 to the Glabra?, recently described by Mr. Etheridge (Q. J. G. S. vol. 



xxxvii. p. 247) in the Vale-of-Wardour " Purbecks." It is true 

 these beds exhibit local unconformities ; but that is natural when 

 freshwater strata succeed marine ; and it is to be noted that " Pur- 

 becks " never lie on any thing but " Portlands." The so-called 

 Purbecks of Swindon and those of Buckinghamshire, lying on lower 



