22 TYPE AMMONITES— IV Dec. 



during the Caloceratan Age. But, later, there is found to be identity 

 of species between B and C and greater equaUty in their respective 

 faunas, which lead to the conclusion that the barrier was ultimately 

 broken down. 



Not quite the same evidence can be brought forward in support 

 of the argument that the Cotteswold area (Juromercia) was a province 

 separated from the Dorset-Somerset area (Jurowessexia). In this 

 case there is no evidence that the Ammonite faunas of the two provinces 

 were distinct — in fact, the evidence, so far as it goes, suggests specific 

 identity. But, south of a line which ran somewhat north of the Mendip 

 axis, there was, during Ludwigian-Sonninian Ages, an Ammonite-fauna 

 of remarkable richness, in excellent preservation. Just a few miles away, 

 north of the line, the Ammonite-fauna is scanty, both in species and 

 in specimens, all badly preserved. Direct communication seems, there- 

 fore, to be ruled out in favour of indirect communication around the 

 island of Juroceltia, to the north of which there was a Hebridean area 

 (Jurhebridea), off the west coast of Scotland, with an abundant, 

 well-preserved Ammonite fauna comparable with that of Jurowessexia. 



Several other facts, however, support this view of an isthmus 

 (Jurobristolia) parting Jurowessexia and Juromercia during Ludwigian- 

 Sonninian Ages. The Brachiopod faunas are different, — as first pointed 

 out by J. F. Walker — ^the strata are quite different, thin in the former, 

 thick in the latter with episodes of brackish water — the Freestones — 

 and with episodes of coral reefs ; the later the strata, the further north 

 of the isthmus is their preservation (Map in S. Buckman, Bajocian of 

 the North Cotteswolds : the Main Hill-mass ; Quart. Journ. Geol. Soc, 

 LXVII, 1901, PI. vi), pointing to a gradual rising along the line of the 

 isthmus ; while, lastly, the further north, that is, the later the deposit, 

 the more abundant are the Ammonites. The strata of the Stepheoceratan 

 Age should have been preserved to the north-west of Cleeve Cloud 

 (Cheltenham), that is, over Worcestershire (see map above cited) : 

 they presumably remained till after Mesozoic times, but were wholly 

 destroyed later. 



Taking Brachiopod faunas and strata as evidence, it seems reasonable 

 to assume that during Ludwigian-Stepheoceratan Ages the Jurassic 

 strata of England were laid down in three, if not four basins : the two 

 provinces already mentioned, Juranglia — Lincolnshire and East 

 England — and Jureboracia — Yorkshire. Jurangha shows brackish 

 water deposits and a micromorph Brachiopod fauna almost wholly 

 unstudied : this area may have been an upper reach — a kind of Gulf 

 of Bothnia appendage — of Juromercia. But Jureboracia, with its rapid 

 alternations of marine and estuarine deposits, cannot be attached to 

 Juranglia — the marine strata demand a position to the seaward, the 

 estuarine to the landward of Juranglia. One or other proposition could 

 be sustained, perhaps ; but alternations of position cannot be. Therefore 

 it appears to be necessary to cut off Jureboracia from Juranglia, giving it 

 the relationship which the White Sea bears to the Gulf of Bothnia, 

 and a similar outlook— to the Arctic Ocean. Many phenomena seem to 

 fit such an assumption, but the difficulty is to find the land whose drainage 

 would make rivers possessing the necessary estuaries, and not to postulate 

 two rivers flowing in opposite directions each side of an anticline, — 

 a kind of Scandinavia— J uropenninia, Scotland and the Pennine 

 range, the highland which stretched down from the north, parting 

 Jureboracia from Jurhebridea. For, though it would not be impossible 



