THE CLYDE TERRITORY. 



407 



tableland may have formed a land-barrier during the beginning of the 

 period, yet as it advanced portions of the tableland were submerged and 

 buried underneath these deposits. 



The various divisions of the Carboniferous system as developed in the 

 West of Scotland are given in the following table : 



'2. Red sandstones, shales, fireclays, and 

 marls, with no workable coal-seams. 

 1. Numerous valuable coal-seams and 



03 



t= 



o 



O 







es 



<J 



O 



Coal-nieasures. 



Upper J 

 Carboniferous. \ 



Millstone 

 Grit. 





Lower 

 Carboniferous.! 



Carboniferous 



Limestone 



Series. 



ironstones, white and grey sand- 

 stones, dark shales and fireclays. 



f Coarse grits and sandstones, with thick 

 beds of fireclay, and occasional thin 

 coals, ironstones, and thin limestones. 



Upper group of three or more lime- 

 stones, with sandstones, shales, and 

 thin coals, including the Castlecary, 



^D / J 



Calmy, and Index limestones 

 descending order. 

 Middle group, with several 



in 



2. 



& roup, with several workable 

 coal-seams and ironstones, sandstones 

 and shales, but no limestones. 

 1. Lower group, with several beds of 

 limestone, sandstones, shales, coals, 

 and ironstones. At or near the base 

 lies the Hurlet limestone. 



Calciferous 



Sandstone 



Series. 



f 



Blue, grey, 



green, 



and red clays, marls, 



shales, and sandstones, with cement- 

 stone bands. (Ballagan series.) 



Reference has already been made to the gradual passage from the Upper 

 Old Red Sandstone deposits to the Cement-stone group at the base of the 

 Carboniferous system in the West of Scotland. But evidence will be 

 adduced to show that in certain areas there is a strong overlap of the 

 succeeding deposits, for the Calciferous Sandstones, Carboniferous Lime- 

 stones, and even the Coal-measures, each in turn rest directly on older 

 rocks. 



The Cement-stone group in the West of Scotland presents uniform litho- 

 logical characters ; the beds consisting of variegated clays, marls, shales, and 

 sandstones, with cement-stone bands which are well exposed in Ballagan Glen 

 near Strathblane. They are comparatively unfossiliferous, but they yield 

 occasionally plant-remains, entomostraca, and fish-scales. Along the north 

 and west sides of the Campsie Fells they are overlaid by white sandstones, 

 and fine tuffs which herald the great outburst of volcanic activity during 

 the Calciferous Sandstone period in Scotland. Indeed this development of 

 volcanic energy rivals in importance the volcanic phase of the Lower division 

 of the Old Red Sandstone. Sir A. Geikie in his recent work on "The 

 Ancient Volcanoes of Britain ;j has depicted the extent of these plateau- 

 eruptions and described the various petrological types which they include. 

 The lavas comprise olivine-basalts, andesites, and trachytes, which are 

 associated with pyroclastic materials. A noteworthy feature is the number 

 of necks or vents now filled with agglomerates or massive igneous rocks 

 from which the volcanic materials may have been discharged, as for example 

 near Strathblane, Fintry, and in Renfrewshire. In the Clyde territory these 

 plateau-eruptions give rise to striking features in the landscape. They form 

 the Campsie Fells, where the terraced appearance of the lava-flows is well 



