582 



J". E. BLAKE 01ST TTIE UPPER 



pendently marked off by a change of fauna, and the " Lower Port- 

 land " comes in in the midst as a true episode. This episode is less 

 marked in the Pays de Bray, and scarcely recognizable in the coast 

 of Kimmeridge, where we find the northern argillaceous type of 

 the Bolonian, equally marked off from the Virgulian by its fossils. 

 During the same epoch the southern or calcareous type was 

 being developed. The distinctions made in this, of lithographic 

 limestones, carious limestones, and tubular limestones, are too local 

 to be of great importance ; but the two zones of Ammonites gigas and 

 either of Pinna suprajurensis or Cyprina Brongniarti are of wider 

 interest. These represent the bulk of the Bolonian in the southern 

 range. It would appear that at Boulogne the argillaceous and cal- 

 careous types overlapped for a while, and the palseontological divisions 

 scarcely coincide with the lithological. Hence if we divide the Bolo- 

 nian into the two parts which have the widest significance, the Lower 

 Bolonian, or zone of Amm. gigas,will commence with M 2 and end above 

 ~N 2 of M. Pellat (that is below the Perna-beds) ; and the Upper Bolo- 

 nian (or zone of Cyprina Brongniarti in the south) will include N 3 

 and JN^ — that is, the remainder of the episode, together with argil- 

 laceous beds called "Middle Portland." M. Pellat includes N 2 also in 

 the upper zone ; but as it contains Amm. gigas the reason of this is not 

 evident. The northern type may also be divided palaeontologically, 

 independently of the forms which may be supposed introduced from 

 the south. The lower portion appears to be characterized by Amm. 

 suprajurensis (formerly quoted as "A. TliurmanniV}, and the upper 

 by several species, amongst which it is difficult to choose the most 

 characteristic. Belemnites SouicJiii, Astarte JScemanni, and Biscina 

 latissima are the chief species almost confined to this portion . These 

 divisions would coincide very nearly with those of the southern range ; 

 and if with the zone of Cyprina Brongniarti were included the un- 

 fossiliferous grey-green limestones of the Meuse and Haute-Marne, 

 the periods might be considered synchronous. This is very nearly 

 the correlation made by Pellat (39, 68) ; that is, he recognized in the 

 two fossiliferous zones his "Lower Portland," and in the barren zone 

 the possible equivalents of his "Middle Portland." His greatest line 

 of division, however, is at a different place, namely above N" 4 . This 

 arrangement may be most suitable for Boulogne ; but it makes the 

 Upper Bolonian almost absent from the southern ranges, whereas it 

 probably continued there in its varied forms long after the intro- 

 duction of clay and clay-loving forms into the Boulonnais. 



Tracing these beds through the areas of their occurrence, 

 we find only the lower Bolonian or lithographic limestones in 

 the Ardennes and Northern Meuse ; and from these the lower 

 portion of the rocks assigned to the same series by Buvignier 

 must be detached, as containing a more Yirgulian fauna, especially 

 Pholadomya acuticostata. The presence of Exogyra virgula itself 

 even in lumachelles cannot be made of any great importance, since 

 at Boulogne, throughout the southern range, and even in England 

 that oyster certainly survived the introduction of a very distinct 

 fauna of far more interest than itself. There is no sign of thinning 



