GEOLOGY FOR CYCLISTS 
23 1 
rocks, the Primary or Palaeozoic, Secondary, and Tertiary 
groups being exposed at the surface in ascending order as we 
traverse the country from west to east. These rocks have been 
sculptured by various physical forces into valleys and dales, 
the higher ground, i.e., that less worn, remaining as plateaux 
and hills ; and the general result is that great diversity of scenery 
which every cyclist admires, but which he should study in con- 
nection with the causes which have produced it. Of these the 
chief have been marine action around the coast, and river action, 
together with rain and chemical disintegration, on the land. Ice 
action also has been a fruitful source of certain phenomena well 
seen in such mountain districts as Snowdonia and Cumberland. 
The town of Penmaenmawr, for instance, stands on the ancient 
terminal moraines of glaciers which came down from the Welsh 
hills and floated away as icebergs to the north ; whilst on the 
other side of the country also are the proofs of sub-marine ice- 
action, the hetips of stones by the roadside, all over Suffolk, 
which are collected off the fields for mending the roads, being 
good epitomes of most, if not all, the strata in England, fragments 
having been brought by ice from the north-east and left at the 
bottom of the sea during the great “ Glacial Epoch.” 
Another class of phenomena are the results of igneous action, 
of which England and Scotland, especially in the west, afford 
abundant illustrations. Thus the two hills Penmaenmawr and 
Penmaenbach are masses of volcanic lava poured out in early 
geological periods, and the gigantic basaltic pillars of the 
Giant’s Causeway and Staffa are some of the last results of the 
great volcanic outbursts which took place all along the western 
coast of Scotland in the early part of the Tertiary period, and of 
which Iceland is the last survival, its volcanoes beings perhaps 
even now the safety-valves of the British Isles. 
The study of these physical phenomena, which are to a large 
extent still in progress, and which in times past have brought 
about the existing features of our island, is now called Physio- 
graphy. It embraces what Sir Charles Lyell called the Principles 
of Geology, a title which he gave to a work which every cyclist 
who wishes to understand geology should study. As a pre- 
liminary, however, he should read Huxley’s “ Physiography,” 
and he might also study the geologically coloured map of the 
environs of London published by Stanford, which exhibits all 
the superficial physical features. This will prepare him for the 
more solid information contained in Sir Charles Lyell’s work. 
The most interesting feature in the study of geology, how- 
ever, is, perhaps, the evolution of life. Commencing with the 
Cambrian, Ordovian and Silurian strata of Wales, we find the 
animal life of those periods all but entirely confined to inverte- 
brates, and although shells and crustaceans attained to enormous 
dimensions, as in the nautilus family and the king-crabs, mere 
bulk is not necessarily a proof of high organisation. The 
gigantic king-crabs of the Silurian, for instance, were lowly 
