Nov. 16, 1882 | 
NATURE 
65 
termination of the glacier. This inference was suggested by the 
consideration that pressure and erosion would be least when the 
glacier was flowing upon a steep slope, while at the base of 
such a slope where the valley flattened ou‘, the ice would tend 
to heap up, as it were, and produce the maximum amount of 
pressure and erosion. Thereafter, as the ice continued to flow 
down its valley, it would become thinner and thinner until it 
reached its termination—and pressure and erosion would diminish 
with the gradual attenuation of the glacier. Such conditions, 
after some time, would necessarily result in the formation of 
elongated rock-basins, sloping in gradually from either end, and 
attaining their greatest depth at some point above a line drawn 
midway between the upper and lower ends of a hollow. There 
are many other details connected with this most ingenious theory 
which I cannot touch upon at present. It will be sufficient to 
say that the observed facts receive from it a simple and satisfac- 
tory explanation. Like all other well-based theories, it has 
been fruitful in accounting for many other phenomena, a study 
of which has developed it in various directions, and enabled us 
to understand certain appearances which the theory as at first 
propounded seemed hardly adequate to explain, As a proof of 
the soundness of Kamsay’s conclusion that ice is capable of ex- 
cavating large rock-basins, I may mention that his theory has led 
to the prediction of facts which were not previously known to 
geologists. He had pointed to the occurrence, in many of the 
sea-lochs of Western Scotland, of deep rock-bound hollows, 
which he concluded must have been formed by great valley- 
glaciers in the same way as the hollows occupied by fresh-water 
lakes in this and other similarly glaciated countries. Some years 
later, having discovered that the Outer Hebrides had been 
glaciate | across from side to side by a mer de glace flowing out- 
wards fi. u the mainland, and having been satisfied as to the 
truth of the glacial-erosion theory, I was led by it to suppose 
that deep rock-basins ought to occur upon the floor of the sea 
along the inner margin of most of our Western Islands. This 
expectation was suggested by the simple consideration that those 
islands, presenting, as they for the most part do, a steep and 
abrupt face to the mainland, must have formed powerful ob- 
structions to the out-flow of the mez de glace in the direction of 
the Atlantic. This being so, great erosion, I inferred, must 
have ensued in front of those islands. The lower part of the 
mer de glace which overflowed them would be forced down upon 
the bed of the sea by theice continually advancing from behind, 
and compelled to flow as an under-current along the inner 
margin of the islands, until it circumvented the obstruction, and 
resumed the same direction as the upper portion of the mer de 
glace, A subsequent careful examination of the Admiralty’s 
Charts of our western seas, which afford a graphic delineation 
of the configuration cf the sea-bottom, proved that the 
deduction from Ramsay's theory was perfectly correct. 
Were that sea-bed to be elevated for a few hundred feet, so 
as to run off the water, and unite the islands to themselves 
and the mainland, we should find the surface of the new- 
born land plentifully diversfied with lakes—all occupying the 
positions which a study of the glaciation of the mainland and 
islands would have led us to expect. Among the most consider- 
able would be a chain of deep lakes extending along the inner 
margin of the Outer Hebrides, while many similar sheets of 
water would appear in front of those islands of the Inner Group 
that face the deep fiords of our western shores. 
The few examples now given of geological methods of inquiry 
may suffice to show that the process of reading and interpreting 
the past in the light of the present necessitates not only accurate 
observation, but an extensive acquaintance with the mode in 
which the operations of Nature are carried on. They also serve 
to show that just as our knowledge of the past increases, so our 
insight into the present becomes more and more extended. For 
if it be true that the present is the key to the past. it is not less 
certain that without that unfolding of the past which a study of 
the rocks has enabled us to accomplish, we should not only miss 
the meaning of much that we see going on around us, but we 
should also remain in nearly complete ignorance of all that is 
taking place within the crust of our globe. Thus, although our 
science may be correctly defined as an inquiry into the develop- 
ment of the earth’s crust and of the faunas and floras which 
have successively clothed and peopled its surface—yet that defi- 
nition is somewhat incomplete. For, as we have seen, this in- 
quiry into the past helps us to understand existing conditions 
better than we should otherwise do. In tbis respect it is with 
geology as with human history. The philosophical historian 
seeks in the past to discover the germ of the present. He tells 
us that we cannot hope to understand the complicated structure 
and relations of a society like ours without a full appreciation 
of all that has gone before. And so it is in the case of geolo- 
gical history. The present has grown out of the past, and bears 
myriad marks of its origin, which would either be unobserved 
or remain totally meaningless to us, were the past a sealed book. 
No student of physical geography, or of zoology and botany, 
therefore can afford to neglect the study of geology, if his desire 
be to acquire a philosophical comprehension of the bearings of 
those sciences. For it is geology which reveals to us the birth 
and evolution of our lands and seas—which enables us to follow 
the succession of life upon the globe, and to supply many of the 
missing links in that chain, which, as we believe, unites the 
beginning of life in the far distant past with its latest and highest 
expression in man. By its aid we track out the many wander- 
ings of living genera and species which have resulted in the 
present distribution of plants and animals. But for geology, 
indeed, that distribution would be for the most part inexplicable. 
How, for example, could we account for the often widely sepa- 
rated colonies of arctic-alpine plants which occur upon the 
mountains of Middle and Southern Europe? How could these 
plants possibly have been transferred from their head-quarters in 
the far north to the hills of Britain, and Middle Germany, to 
the Alps and the Pyrenees? Not the most prolonged and labo- 
rious study of the botanist could ever have solved the problem. 
But we learn from the geologist that the apparent anomalous 
distribution of the flora in question is quite what his study of 
the rocks would have led him to expect. He now, indeed, 
appeals to the occurrence of those curious colonies of arctic- 
alpine plants as an additional proof in support of his view that 
during a comparatively recent period our continent experienced 
a climate of more than arctic severity. He tells us that at that 
time the reindeer, the glutton, the arctic fox, the musk ox, and 
other arctic animals migrated south into France, while a Scandi- 
navian flora clothed the low grounds of Middle Europe. By 
and by, when the arctic rigour of the climate began to give way, 
the northern species of plants and animals slowly returned to 
the high latitudes from which they had been driven. Many 
plants, however, would meet with similar conditions by ascend- 
ing the various mountains that lay in the path of retreat, and 
there they would continue to flourish iong after every trace of 
an arctic-alpine flora had vanished from the low ground. This 
explanation fully meets the requirements of the case. It leaves 
none of the facts unaccounted for, but isin perfect harmony with 
all. But as if to make assurance doubly sure, Dr. Nathorst, a 
well-known Swedish geologist, recently made a search in the 
low grounds of Europe for the remains of the arctic-alpine flora, 
and succeeded in discovering these in many places. He de- 
tected leaves of the arctic willow and several other characteristic 
northern species in the glacial and post-glacial deposits of 
Southern Sweden, Denmark, England, Germany, and Switzer- 
land, and thus supplied the one link which might have been 
sidered necessary to complete a chain of evidence already 
almost perfect. 
From this and many similar instance that might be given we 
learn that the reconstruction of the past out of its own ruins is 
not mere guess-work and hypothesis. The geologist cannot 
only demonstrate that certain events have taken place, but he 
can assure us of the order in which they succeeded one after the 
other, during ages incalculably more remote than any with which 
historians have to deal. The written records out of which are 
constructed the early history of a people cannot always be 
depended upon—allowance must be made for the influences that 
may have swayed the chroniclers, and these are either unknown 
or can only be guessed at. It follows therefore that events are 
seldom presented to us in a consecutive history exactly as they 
occurred. They are always more or less coloured, and that 
colouring often depends fully as much upon the idiosyncrasies of 
the modern compiler as upon those of the contemporaneous 
recorder. The geologist has at least this advantage over the 
investigator of human history, that his records, however frag- 
mentary they may be, tell nothing more and nothing less than 
the truth. Any errors that arise must be due either to insuffi- 
cient observation or bad reasoning, or to both, while the pro- 
gress of research and the penetrating criticism which every novel 
view undergoes must sooner or later discover where the truth 
lies. In this way the history of our globe is being gradually 
reconstructed—to an extent, indeed, that the earlier cultivators 
of the science could not have believed possible. But although 
