102 Tail GEOLOGlSl^. 



beneath us as having been subjected to many vicissitudes, and to frequent 

 and more or less vast and important fluctuations of level ; that, some- 

 times above the waters, it has been clothed with vegetation and with 

 appropriate forms of animal life, and sometimes beneath the waves, 

 fresh sediments, enclosing the creatures of the deep, have covered the 

 terrestrial conditions that were; and then again uplifted, the new 

 deposits have been covered with verdure, and fresh forms of living 

 creatures have appeared, 



A glance at the section (p. 93) will show that, for the purpose for which, 

 at my request, my talented and highly-valued friend, Mr. T. Eupert 

 Jones, designed it in connection with these papers, it is necessary 

 only there to indicate the great disturbances which affected our own area 

 during the Silurian period, and those other great disturbances by 

 which the Paloeozoic period was terminated and cut off from the 

 Secondary or Mesozoic period, which succeeded it. In the grand se- 

 quence of events there displayed, we have, first, the gneiss and "bottom 

 rocks" upheaved ; then a sinking of the land for ages, with accumula- 

 tions of sediments ; a counter-upheaval of a large tract, with a general 

 denudation of the surface followed by a continued gradual subsidence of 

 the whole, with more and more deposits, continued up to the period when 

 the sediments had well filled up extensive portions of the ancient 

 sea-bed, forming low banks and islands, and sestuarine and land-lock 

 coasts, on and around which the gigantic vegetation, which the warm 

 and humid atmosphere nourished and fostered, grew in wild luxu- 

 riance, and, mingling with the drifted trees and plants brought by 

 the rivers and currents to the tranquil bays, formed part of that 

 great accumulation of vegetable matter which has been since, by 

 the chemistry of nature, elaborated into that wonderful and invalu- 

 able mineral, coal. After the deposition of the coal-measures, 

 something like the ancient conditions returned ; the new red sandstone 

 formation spreading out above them, so like the old red sandstone 

 scries beneath in its marls and conglomerates, that only by position 

 and by the difference of the creations each has entombed, can the one 

 bo distinguished from the other. With the Permian catastrophes 

 oar share in the first world ended. But these catastrophes were not 

 universal. The disturbances which have made the line of demarcation 

 between the primary and secondary groups of rocks so strong in our 

 own island, were limited in their area and in their effects. In other 



