156 INVERTEBRATE PALAEONTOLOGY 



and only occasional inroads of marine conditions reached 

 the Midlothian " lake-basin." However, proximity of 

 the sea induced climatic changes there ; the " Coal- 

 Measure " conditions of the Calciferous Sandstone stage 

 are in marked contrast to the desert features shown 

 by the Upper Old Red Sandstone. Meanwhile, the 

 " Devonshire " area seems to have undergone varied 

 and violent changes of level, resulting in the complex 

 rock-series of the Culm Measures, which contain Radio- 

 larian cherts indicative of deep water, and Anthracitic 

 material suggestive of almost terrestrial conditions. 



The brief success of the Carboniferous Limestone 

 sea in invading " Lake Caledonia " was followed by 

 diversion of a vast amount of sediment on to the British 

 area. Sand-banks and mud-flats began to spread 

 southwards from the Cheviots, silting up the sea-basin 

 and smothering islands that had defied the sea itself. 

 Gradually these deposits produced a delta-, from whose 

 marshy flats marine conditions were eventually excluded. 

 Marine bands, often crowded with fossils, occur in the 

 Lower Coal Measures, but such intercalations are rare 

 in the main parts of the coal-bearing strata. 



A fresh paroxysm of upheaval, the " Pennine Uplift," 

 began to affect the British area before the end of the 

 Coal Measures, and continued more or less persistently 

 throughout the Permian. On the western side of the 

 Pennine chain, topography reminiscent of parts of the 

 Old Red Sandstone land-area was produced, resulting in 

 lacustrine marls and " brockrams " fallen from fault- 

 scarps or volcanic peaks. The vast plutonic intrusions 

 of Devonshire and Cornwall belong to this episode; 

 their development mutilated and metamorphosed all 

 earlier rock-systems of that district. On the eastern 

 side a synclinal depression (complementary to the 

 Pennine anticline) let in a gulf of the sea in North- 



