40 
Apennines, Pyrenees, Carpathians, all belong to one or other of 
the tertiary ages. The plants and animals become more like 
those now living as the primary formations are the ages of 
brachiopods, the secondary the age of reptiles, then the last is 
the age of mammalia. In the second or Miocene age the volcanic 
forces again burst out with terrible energy. In the islands of 
Mull and Skye are the remains of two large volcanoes rising to a 
height of 8,000 feet in some places. The tops liave been denuded 
away. The diameters at the bases are about 30 miles, and the 
heights, when in their undenuded state, was, one 10,000 to 
12,000 feet, the other 14,000 to 15,000 feet. In the north of 
Treland the sheets of volcanic strata form beds 500 to 600 feet 
thick, and 1,200 square miles in area. The Giant’s Causeway 
and Fingal’s Cave belong to this period. The line of volcanic 
action was north through the Hebrides to Iceland. Innumerable 
trap dykes (or walls of igneous rock) running with an east and 
west trend have cut through all the formations up to and includ- 
ing the chalk and cross faults of every size that come in their 
way. Sometimes they go for 200 miles in almost a straight line, 
turning neither to the right nor left, but breaking through all 
rocks alike. The members will remember one of these dykes 
which we saw in Teesdale during the society’s excursion. These 
also were of the miocene age. All these volcanoes are now dor- 
mant, yet now and again we have a slight shake, reminding us 
that we live upon the line of volcanic action. At each end of 
the line furious eruptions are constantly taking place—Iceland 
and Sicily probably acting as safety valves and allowing the forces 
to spend themselves, and keeping us free. Thus for years untold, 
England has been without any eruption, and with very little 
of the shaking which accompanies volcanic action. What 
guarantee, however, have we that they will not again break out ? 
I say the guarantee given by occasional trembling of the earth, 
or the water at Buxton, Bath, and other places rising to the 
surface heated by the lingering fire. The guarantee also that 
the knowledge that the distance in time from us to the eruptions 
of Mull and Skye, is but as yesterday compared with the time of 
quietude between the tertiary and primary periods, and that after 
even that long rest the fires burst forth, and that we are still 
living in the tertiary period, perhaps the most terrible of all the 
voleanic periods of our island’s history. 
