CHAP. I.X 
GEOLOGICAL PIONEERS IN WALES 
43 
At the outset of the following discussion I wish to express iny admiration 
of the labours of the early pioneers who thus laid for us the foundatiou of 
our knowledge of volcanic action in the Paheozoic periods. To De la Beche 
and his associates in the Survey a special measure of gratitude is due from 
all who have followed in their steps and profited by their work. AVhen we 
consider the condition of geological science, and especially of the department 
of petrography, in this country at the time wlien these early .and detailed 
investigations were carried on, when we remember the imperfection of much 
of the topography on the old one-inch Ordnance maps (which were the only 
maps then available), when we call to nund the rugged and lofty natrue of 
the ground where some of the most complicated geological structures are 
displayed, we must admit that at the period when these maps and sections 
were produced they could not have been better done ; nay, that as in some 
important respects they were distinctly in advance of their time, their 
publication marked an era in the progress of structural, and especially of 
volcanic, geology. The separation of lavas and tuffs over hundreds of 
square miles in a mountainous region, the discrimination of intrusive sheets 
and eruptive bosses, the determination of successive stratigraphical zones of 
volcanic activity among some of the oldest fossiliferous formations, were 
achievements which will ever place the names of Eamsay, Selwyii, Jukes 
and their associates high in the bede-roll of geological science. No one 
ever thinks now of making a geological excursion into Wales without 
carrying with him the sheets of the Geological Survey map. These form 
his guide and handbook, and furnish him with the basis of information from 
which he starts in his own researches. 
But science does not stand still. The most perfect geological map that 
can be made to-day will be capable of improvement thirty or forty years 
hence. The maps of the Geological Survey are iio exception to this rule. 
In criticizing and correcting them, however, let us judge them not by the 
standard of knowledge which we have now reached, but by that of the time 
when they were prepared. It is ea.sy to criticize ; it is not so easy to 
recognize how much we owe to the very work which we pronounce to be 
imperfect. 
The ancient volcanoes of Wales, thanks mainly to the admirable labours 
of my former friend and chief, Sir Andrew C. Karasay, have taken a familiar 
place in geological literature. But a good deal has been learnt regarding 
them since he mapped and wrote. The volcanic history, as he viewed it, 
began in the Arenig period. The progress of subsequent inquiry, however, 
iras shown that there are volcanic rocks in Wales of much older date. I 
shall show that the Cambrian period, both in South and North Wales, was 
eminently volcanic. 
Much controversy having arisen as to the respective limits and nomen- 
clature of the older Palajozoic rocks, let me state, at the outset of the 
inquiry into the volcanic eruptions of Cambrian time, that under the term 
Cambrian ” I class all the known Palfeozoie rocks which lie below the 
bottom of what is termed the Arenig group. It was maintained by Sir 
