The Buried Palaeozoic Rocks of Wiltshire. 81 



however, is not such plain sailing, and you will see that although 

 Sectiou B is placed under Section A., and although the rocks really 

 do underlie those of the upper section, yet the beds are differently 

 inclined, and do not follow the upper rocks or each other in the 

 same regular way. To this point I want particularly to call your 

 attention, since it has an important bearing on the position of the 

 coal measures and their relations to the overlying strata, as also to 

 probability of their being found under Westbury or not. The 

 inclination, or dip, and succession of the upper rocks in Section A. 

 we know from finding them at the surface, and from the evidence 

 of wells, bore-holes, &c, which have been made in them from time to 

 time. But the relative position and inclination of the beds in 

 Section B. are matters of inference, not of observation, and conse- 

 quently are far less certain. Of their existence before the newer 

 rocks were laid over them there is no doubt, but which of them 

 occur under any particular spot, and how much of them remain, is 

 quite another matter. 



C. is a section across the country from Westbury to Vallis Yale, 

 near Frome, and represents the structure that might be made visible 

 if a long and deep trench could be cut through the earth's crust 

 along this line. Here the upper rocks (neozoic) are seen deposited 

 in regular order and sequence, all with the same inclination, or dip, 

 while the lower (palaeozoic) show a different inclination and are very 

 irregular. These upper and lower beds having no regular sequence 

 and apparently no relative connection with each other, are said, in 

 geological language, to be unconformable. 



The three maps, marked respectively I., II., and III. (which Mr. 

 Jukes Brown, F.G.S., of the Geological Survey, has kindly placed 

 at my disposal, being taken from his work, " The Building of the 

 British Isles are intended to show the geography of the British 

 Islands at the different geological periods named on the maps ; the 

 part coloured with blue lines being the ancient seas, the uncoloured 

 portions the then existing land ; while the faint red lines show the 

 present outline of the land. 



I must now go back to the close of palaeozoic time — to that period 

 which is called Triassic or Permian. This commenced after a long 



VOL. XXV. — NO. LXXIII. G 



