CHAP. III.] ORDOVICIAN PERIOD. 31 



muddy deposits representing the lower part of the Ordo- 

 vician system that part of the Skiddaw slates which 

 underlies the grit-beds of Gatesgarth and Latterbarrow 

 being 4,000 or 5,000 feet, and that above these grits being 

 no less than 7,000 feet thick. These are succeeded by an 

 immense series of lavas and ash-beds with interbedded 

 slates (the Borrowdale series, estimated at 12,000 feet), 

 above which are limestones and shales, which correspond 

 to the upper part of the Bala group of Wales. 



With regard to the Skiddaw series, Mr. J. C. Ward l re- 

 marks that the grits in the lower part of the series thicken 

 to the westward, whence he infers that continental land 

 lay in that direction. The water in which the material of 

 the slates subsided was probably never very deep, and 

 there must have been a long-continued depression of the 

 area to allow of so thick an accumulation of sediment. 

 Mr. Ward states that in the south-west of the district the 

 volcanic forces came into play much earlier than they did 

 to the north-east. It is also known that in some places the 

 Limestone group rests unconformably on the volcanic 

 series. 



The following paragraphs are quoted from Mr. Ward's 

 paper. The observed facts " all point to volcanic action 

 commencing at the close of the so-called Skiddaw slate 

 period beneath the waters of the sea, and the gradual pas- 

 sage from submarine volcanic conditions to those of ter- 

 restrial and wholly subaerial volcanoes. 



"The centres of eruption are difficult to fix upon, as 

 might be expected amongst volcanic remains of such anti- 

 quity. The boss of Castle Head, Keswick, almost certainly 

 represents one such centre, and the best developments of 

 lava flows are all found occurring within easy distance. . . . 

 What the height of the old Cumbrian volcano or volcanoes 

 may have been it is difficult to estimate, but volcanic de- 

 1 "Geol. Mag.," 1879, p. 51. 



