Chap. 12.] GEOLOGY, BOTANY, &o. 255 



silting up, another luxuriant growth of vegetation, another submer- 

 sion, and so on, with varying intervals, until twelve thousand feet of 

 sedimentary matter had been deposited and nearly one hundred beds 

 of vegetable matter had grown and been buried. During the periods 

 of terrestrial conditions there was a gradual development of air- 

 breathing animals. The remains of huge batrachians and of one 

 hundred and fifteen species of insects have been found. 



Our largest coalfield is that of South "Wales, with an area of 900 

 square miles. It contains 75 seams of coal, varying in thickness from 

 3 to 9 feet, with a total depth of 120 feet of coal. The total depth of 

 the strata containing these beds is estimated by Prof. Hull at 11,650 

 feet. The same authority, estimating the increase of sediment at two 

 feet in a century, and allowing 1,000 years for the growth of the 

 vegetation required to form three feet of coal, has calculated that the 

 deposits forming the South Wales coalfield might have been 

 accumulated in 640,000 years. 



Shortly after the close of the Carboniferous period, the British area 

 appears to have been subjected to great lateral strain in an easterly 

 and westerly direction. There was a general upheaval of the land, 

 and the Pennine Eange was formed. At the same time, or later, there 

 appears to have been a lesser strain exerted at right angles to the 

 main one, and this resulted in the formation of a series of smaller 

 anticlines, branching fi-om the central one. In the hollows between 

 these hills, inland seas and lakes were enclosed, in which were de- 

 posited the red sandstones and magnesian limestones of the Permian 

 System. One of these lakes probably extended over the whole of the 

 north of England and embraced parts of the south of Scotland. 

 Portions of the deposits have, however, been subsequently removed by 

 denudation, and other portions are covered by more recent deposits. 

 None occur near Longridge, but the red sandstones occur near Brock 

 Eailway Station, atGarstang (see Plate 1), and a small patch at Eoche 

 Bridge, near Walton-le-Dale. During Permian times, and subse- 

 quently, the coal-measures, wherever they covered the recently-formed 

 hills, were favourably exposed to the utmost forces of atmospheric 

 denudation, while those portions which foi-med the low-lying lands 



