CHAP. VII.] DTASSIC PERIOD. 109 



are parallel to the central Pennine axis, we may safely 

 assume that they were both formed at the same time. 



2. After crossing the Millstone Grit area of central 

 Yorkshire, the outcrop of the Dyas again passes on to 

 Coal-measures in the south of Durham, showing that 

 all the flexures between the two coal-basins were pre- 

 Dyassic. 



3. No Dyassic outliers occur at any distance west of the 

 main escarpment, and no fragments of Magnesian Lime- 

 stone have been found in the Triassic rocks, as might 

 have been expected if that limestone had passed over the 

 Pennine axis, and had been subjected to erosion in Trias- 

 sic times. 



4. On the other hand, fragments of Carboniferous Lime- 

 stone are said to have been found both in the Dyassic 

 breccias and in the Triassic sandstones, which would prove 

 that this limestone had already been bared along the 

 Pennine axis. 



5. The Dyassic rocks on opposite sides of the Pennine 

 range are very dissimilar, the thin local beds of niagnesian 

 limestone on the western side bearing no comparison with 

 the massive dolomites of the eastern tract, while the red 

 sandstones are essentially a feature of the western dis- 

 tricts. 



It might perhaps be doubted whether the range formed 

 a complete barrier, and whether there was not communica- 

 tion between the two areas of deposition by means of a 

 narrow strait across the centre of Yorkshire. The only 

 piece of evidence in favour of such a communication is the 

 occurrence of Magnesian Limestone fossils in the lime- 

 stones of Lancashire and Ireland, but as both the eastern 

 and western areas were uplifted portions of the Carboni- 

 ferous sea, the same forms of life are likely to have re- 

 mained in both, even if one was rapidly isolated by the 

 upheaval of a barrier. On the whole, therefore, the 



