Page:Early Man in Britain and His Place in the Tertiary Period.djvu/74

46 extent and elevation. The granites of Arran, and, in Ireland, those of the Mourne mountains and the basalts of Antrim, are also referred to the same age. Thus, in the Meiocene age, along a line of 400 miles from north to south in the British area, there rose a chain of lofty and active volcanoes, on a scale comparable to those of the Andes, overwhelming from time to time with their lava and ashes the Meiocene forests in their vicinity. This line of ancient volcanoes is continued northwards into the Färoes, Iceland, and Greenland.

The present state of these volcanoes affords us a means of measuring the destruction of rock in the post Meiocene times. In Fig. 7 the dotted line represents the outline of the Meiocene surface, while the actual surface is shown by the continuous line. Not only have their cones disappeared by the action of the elements, but the more solid accumulations forming their bases have been reduced to mere fragments during the untold ages which have passed away since they were active. Since they have lost more than one half of their former height, it is reasonable to suppose that similar amounts of rock have been removed from other areas in Great Britain, the greatest destruction being wrought on the flanks of the mountains, and the least on the slopes near the sea level. Under these circumstances, we could not expect that any traces of the old Meiocene land surface or river deposits should be preserved to the present day, excepting under very unusual conditions. They for the most part have been swept away, along with a flora and fauna probably