‘240 
WA TORE 
ce did not recede gradually, because it would not then 
have left behind such great ramparts, but the sand and the 
gravel would have been spread more evenly. During the 
melting, however, its edge remained at times stationary, 
or advanced perhaps a little. At each such event a row 
of moraines was formed, and as the same are found in 
large tracts of the country, they cannot be attributed to 
local circumstances, but we have to assume ¢hat periodical 
variations of climate were the cause of the manner in 
which the tce receded. 
We found in the peat-bogs alternately layers of different 
kinds, peat alternating with remains of forests several 
times, and we saw how this was easiest explained by 
periods of change in the climate. But these alternating 
layers are not peculiar to the peat alone, but found in ali 
stratified formations, loose as well as solid, whether de- 
posited in fresh or salt water, or on land, in all the strata 
from the Laurentian gneiss to the loose deposits of the 
present age. Take a geological structure from any age, 
alternating layers will be found everywhere. Sand alter- 
nates with gravel, sandstone with conglomerate, clay 
with sand, slate with sand or sandstone, marl with clay, 
chalk with marl, and so on. The layers vary in thickness, 
from several yards to less than an inch. 
The solid rock withers away by the action of air and 
water in heat and cold; it partly crumbles away mech- 
anically and partly changes chemically. The products 
of the erosion are carried by wind or running water as 
dust, in dissolved or original state, and deposited in places 
more or less remote from those where they were produced. 
The foaming mountain stream often carries great stones 
in its course, and the softer the wind and the weaker the 
current the finer is the matter deposited. When the 
current becomes weak the gravel sinks first, then the sand, 
then the clay, and, finally, the chemically-dissolved lime 
by the animal life in the water. When we, therefore, have 
a change of beds of different composition through all 
geological ages,as those mentioned above, it must be due 
to the circumstance that the speed of the depositing 
stream was always varying—now increasing, now de- 
creasing. 
The Challenger Expedition has taught us that all the 
stratified rocks which geologists hitherto have known 
must have been formed comparatively near the shore, even 
if deep-sea formations. They are all of quite a different 
nature from the strata in the abysses of the great oceans. 
From this it follows that the variations in the rainfall might 
have had some influence on the nature of the strata in 
the known geological formations, since they were formed 
comparatively near land and are the result of the erosion 
of the solid rock. A weak river is unable to carry debris 
far out to sea, but a strong one is capable of supplying 
the sea-currents with deposits over great areas. When, 
therefore, the rivers alternately increased and decreased, 
the sand, clay, and gravel were carried now a greater, now 
a less distance, into the sea, and thereby the variations of 
the layers were produced. 
It is, however, not the intention to assert that all alter- 
nations of layers are due to that long climatic period. 
When the stratification goes on quickly, and the supply of 
matter is plentiful, rapid local changes may produce an 
alternation of strata. In the Norwegian marl-clay, 
formed during the melting of the inland ice, alternating 
thin layers of sand and clay are found, varying in colour, 
sometimes only a quarter of an inch in thickness or even 
less. These variations must be ascribed to changes 
during brief spaces of time, and cannot be referred to 
the long climatic periods. But, of course, such layers 
are only formed in the immediate vicinity of the coast, 
and during the constant advance and retrogression of the 
latter, which may be traced through all geological ages, 
such shore-formations were most exposed to destruction. 
They were frequently lifted above the sea, and were more 
exposed to the destructive agencies—air and currents— | 
than those formed in 
deeper waters further from the 
shore. For this reason these quickly-formed layers have 
at all times been more exposed than others to destruc- 
tion, and we must, for that reason, conclude that most 
of the beds which constitute the geological stratified 
deposits were formed somewhat further from the shore, 
and that, consequently, the time of their formation was 
longer. From the thickness of the layer alone it is im- 
possible to form an idea of the time it has taken to form, 
because in the time a layer in one place upwards of several 
yards in thickness has been forming, only an inch has 
formed in another, whilst in a third place in the same 
time the formation has ceased, or older layers even carried 
away. But we have a means whereby we may ascertain 
the time it has taken to form a layer, viz. the study of the 
remains of the flora and fauna found in the same. The 
most frequent species have, cefer?s paribus, the most 
chance of being preserved. When, therefore, we find 
that fossils, as is often the case, vary from stratum to 
stratum, we must assume that this proves that great 
changes took place in the fauna and the flora during the 
formation of each stratum. What was stated above with 
regard to the variations in the peat-bogs of remains of 
plants from layer to layer #ay be applied to variations af 
strata through all ages. The examination of the fossils 
in the strata teach us respect for Time. The fossils vary 
quickly even in strata of smal] thickness. In one stratum 
we find remains of distinct animals and plants, and in 
the one above—although, perhaps, only an inch above it 
—we find others quite different. A thin stratum of a 
couple of inches is sometimes distinguished by peculiar 
animals and plants, so that the stratum may be recognised 
over large areas by the aid of the same. When two strata 
of different nature alternate, it is generally found ¢hat one 
hind of stratum contains certain fossils, and that those of the 
others are quite different. The theory of periodical varia- 
tions of the climate erflains all this. Because if the sea- 
currents varied in strength, the temperature of the water, 
and consequently the aquatic fauna and flora, must have 
changed too; with a higher temperature of the sea the 
moisture of the air and the rainfall] must have increased, 
and thus a periodical change of the sea-currents would 
have the effect of causing variations of the strata. It is 
exactly such strata of varying nature, and varying forms 
of fauna and flora, which would build the geological 
strata of the earth. 
We have seen how this theory explains a number of 
various well-known puzzles to scientific men, viz. the 
scattered extension of species of plants and animals ; the 
formation of the terraces of shell-banks and_ shore- 
lines ; the rows in which moraines appear ; and, finally, 
the alternation of peat-layers and various geological 
strata. It only remains now ¢o find a natural cause for 
such a periodical variation of the climate, but before 
doing this it is necessary clearly to understand what 
the theory demands. 
It does not require great changes ; all the facts on 
which it is founded may be explained by comparatively 
small variations in the extremes of temperature and rain- 
fall. No very great variation is required in order that 
the holly and similar coast-plants should be able to grow 
by the Christiania fjord, as the theory assumes it once 
did; because the holly, which cannot stand the winter 
cold at Christiania (lat. 60° N.), has for many years been 
successfully cultivated in the open air at Horten, only half 
a degree further south on the samefjord. And along the 
[Fuly 15, 1886 
coast plants of Oriental origin have, during the last 
thousands of years, spread from the Christiania and 
Throndhjem fjords right out to the open shores of Jaederen 
and Fosen, the former in lat. 58°-59° and the latter in 
lat. 63°-64° N., and there would hardly be required a very 
great change to enable them to grow also in the inter- 
vening district, the province of Bergen, which would 
again make their extension continuous. 
