584 



J. P. BLAKE ON THE TJPPEE 



of the blue marls called " Middle Portland." The latter undoubtedly 

 correspond to the beds called by the same name at Boulogne ; and 

 the grits below represent the upper part of the so-called " Lower 

 Portland," as has been shown by Pellat (46). 



In our own country the Bolonian strata are pretty nearly synony- 

 mous with those shown to be separable under the title Upper 

 Kimmeridge. Only in the coast-section of Dorsetshire has any dis- 

 tinction into Upper and Lower Bolonian been possible as yet ; but 

 when once it is recognized that the whole is argillaceous, the two 

 parts may be some day recognized by their fossils. Throughout the 

 basin of Paris, however, and in the Dorset section, the lower beds are 

 less fossiliferous, and therefore in England they will be less likely 

 to attract attention in inland sections. In separating the Bolonian 

 from the Kimmeridge below and the Portland above, there arises in 

 England, as at Boulogne, the question as to their limits. In the 

 latter place, the " Lower Portland " is taken by Pellat (68) to com- 

 mence in the midst of marls, on account of the change of fauna. 

 And this change is a remarkable one ; for it consists in the intro- 

 duction of species which do not specially characterize the episodal 

 deposits, but which continue upwards through the whole of the 

 Bolonian. So on the coast of Dorset the lower limit of the Bolonian 

 must also be drawn in the midst of clays, where the most marked 

 introduction of new species commences. This takes place at no very 

 well defined line ; so that the limit must remain open ; in any case 

 it will be below bed No. 29 of the.Kimmeridge Bay section, and may 

 be as low as No. 40. At Boulogne, the "Middle Portland " has been 

 taken to end upwards where "the sands cease to be marly and are 

 often consolidated into calcareous grits, the lowest beds of the next 

 series containing a different fauna, the most remarkable species being 

 Cardium Pellati. If we draw the same line in England, it will 

 lie immediately beneath the Flinty series of the coast, the Tisbury 

 freestone, the Swindon Trigonia-beds, and the rubbly limestones of 

 Buckinghamshire. In other words, the "Portland Sand" must be 

 thrown into the Upper Bolonian, care being taken that the glau- 

 conitic and rubbly beds which form the base of the true Portland 

 are not included. That the sands ought to be separated from the 

 Portland Stone was perceived by Eitton ; and their distinctness from 

 the general mass of the Kimmeridge Clay, was equally clear to him. 

 The fact of their containing a fauna muck ' allied to that of the 

 higher parts of what was then called the Kimmeridge Clay, enables 

 us rightly to associate the two under a separate and common title, 

 the Bolonian. This period both in England and the North of 

 France, served as an introduction to the Portland, with the lowest 

 beds of which its uppermost strata have several fossils in common. 



The localities in England which show Bolonian strata may now 

 be enumerated. In general, of course, all that has been described 

 as Portland Sand will now represent part of the Upper Bolonian, 

 and, in addition, much that has been termed Kimmeridge Clay. The 

 brick-yards at Upway, the fossiliferous beds at the base of the Tis- 

 bury section, the sandy " Kimmeridge Clay " of Devizes, so rich in 



