Gravitation as a Factor 
34 
[January, 
entered the German Ocean, and pass obliquely over the flat 
lands of Caithness.'*' 
The accompanying Chart, reproduced from “ Climate and 
Time,” shows the probable path taken by the ice in its out- 
ward motion from these two centres of depression. The 
Chart, it is to be observed, is not theoretical, for the lines 
represent the actual direction of the striae on the rocks. It 
was inadequate conceptions of the nature of continental ice 
which prevented geologists from coming to the conclusion 
that all those striae were produced by land ice. 
II. GRAVITATION AS A FACTOR IN THE 
ORGANIC WORLD. 
By William Crookes, F.R.S. 
Cif. 
* T cannot be denied that in discussing the great questions 
v ^ of the origin of life and the development of species, — 
in seeking to explain to ourselves why every creature 
is as we find it, and not otherwise, — we have to deal with 
two sets of faClors. 
On the one hand we have certain outward agencies, such 
as the great cosmic forces, the chemical and physical cha- 
racter of the earth’s surface and of its liquid and gaseous 
envelopes, the varying effedts of climate, the quality and 
quantity of food accessible, the conflict with other species, — 
everything, in short, which the animal encounters either as 
an enemy or as an ally in its struggle for existence. 
On the other hand, there are doubtless inward tendencies 
upon which these external forces reaCt. For if we see a roll 
of calico passing through a dye-bath of alizarin, and coming 
out not all of one uniform shade, but displaying a parti- 
coloured pattern, we know that different mordants must have 
been imprinted upon it with each of which the dye gives a 
different result. Just so here ; were the outer fadors alone 
present, no variety could result from their aCIion. But of 
* An important paper by my colleagues, Mr. B. N. Peach and Mr. J. Horne, 
on the Glacial Phenomena of the Shetland Islands, will shortly be read before 
the Geological Society of London. They have found evidence which puts the 
question beyond all doubt that the whole of those islands have been glaciated 
by land*ice from Scandinavia. 
