The Buried Paleozoic Rocks of Wiltshire. 81 
however, is not such plain sailing, and you will see that although 
Section 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, aud how much of them remain, is 
quite another matter. 
C. is a section across the country from Westbury to Vallis Vale, 
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 (palzeozoic) show a different inclination and are very 
irrevular. 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 paleozoic time—to that period 
which is called Triassic or Permian. ‘This commenced after a long 
VoL. XXV.—NO, LXXIIL G 
