144 
POPULAR SCIElsrOE iTEWS. 
[October, 1891 
When the blades at last open through their own 
impulse, the viscid secretion of digestion has dis- 
appeared ; the leaf is dry, clean, and briglit ; the 
dissicated skeleton of the fly is ejected, and some- 
times it is found to have been so flrmly pressed 
between the blades as to leave its impression in- 
dented line for line, with great accuracy, upon 
their aoft substance. — 
The Dionxas will accept artificial feeding, and 
as readily digest some of the articles eaten by 
man as their own more usual diet of insects. Milk 
they seem to really relish, and in their leafy stom- 
achs it speedily resolves itself into the orthodox 
curds and whey, which are afterwards absorbed — 
some nine days being required to dispose of the 
curdy part. But while milk seems to aflbrd suita- 
ble nourishment, — unless given in too great quan- 
tity, — cheese they do not tolerate at all, the leaf 
to which it has been fed turning black and dying 
upon every occasion, whether the article oflered 
was newly made or of the ancient and mouldy 
class. Salt, so grateful to the human stomach, 
proves a positive poison to these vegetable ones. 
The boiled white of an egg, however, they find 
quite to their taste. Small bits of raw beef are 
also accepted and apparently digested. When, 
after having been for two or three days exposed 
to the action of the digesting fluid, these morsels 
were removed from -the leaf, they were found to 
have become white, tender, and easily macerated, 
and showed not the least tendency toward a pu- 
trid decomposition. 
The Venus fly-traps are, however, by no means 
of a glutton-like habit, and a leaf which is overfed 
will surely die. But they generally know when 
they have had enough, and can no longer be 
tempted, the sensitive hairs refusing to respond, 
no matter how cunningly they may be manipu- 
lated. Another idiosyncrasy of the plant is that 
it prefers the victims of its own bow and spear to 
any that may be captured for it ; and it manifests 
something very like intelligence in its quiet ))ut 
persistent rejection of practical jokes ofTered in 
the guise of small pebbles, grains of sand, and 
other substances impossible to its digestion. In- 
deed, it may be termed truly refined in its tastes, 
when compared with other fly-catchers, notably 
the Sarracenia. These plants, after capturing 
their food in immense quantities, and of any sort 
that comes to hand, leave it to putrify within 
their pitcher-like receptacles, which reject noth- 
ing ; and the plants subsist and thrive finely upon 
this revolting mass, which makes itself manifest 
by its foul odor for some distance around. Our 
Dionaea, on the other hand, being, perhaps, — who 
shall say? — under some subtle influence emanating 
from the lovely goddess whose name it bears, is as 
tidy in habit, as fastidious in taste, as the most 
dainty of women. It closes its leaves, it is true, 
upon any foreign substance that may be placed 
within them, responsive, always, to the irritation 
of the hairs; but unless it finds the matter en- 
closed in its emt)race to be suited to its tastes or 
needs, it is as sure to be expelled as if the plant 
was possessed of reasoning power. 
When the experiment was tried of cutting oft' 
the sensitive hairs, and thus removing them al- 
together from the leaf, it was followed at first by 
its closing. After a while it opened again, and 
then the action became as truly capricious as if 
the plant was endowed with will power. Some- 
times the leaf failed to respond at all when irrita- 
tion was applied to the parts where the hairs had 
been; at others, the two halves came together 
just as they do when all is perfect; again, the 
action followed slowly and awkwardly when a 
considerable time had elapsed after the Irritation 
had ceased ; and sometimes the two blades failed 
to act in concert. But, perhaps, no one of these 
variations is as difficult to account for as the fact 
that the leaf should close at all when thus crip- 
pled in its motive power. 
«♦* 
[Original in Populab Sciencb News.] 
GLACIERS. 
BY JOSEPH WALLACE. 
With the development of science a correspond- 
ing growth of theories takes place. In truth, we 
theorize too much, and endeavor to draw conclu- 
sions from far-fetched ideas for the purpose of 
upsetting preconceived theories and notions well 
founded. The theory of a glacial period, or Ice 
Age, has developed many absurd hypotheses; 
and though accepted by scientists and the learned 
of all civilized countries, with a few unimportant 
exceptions, all do not agree on its extent and du- 
ration. 
Under the name glacial period a remarkable 
episode in the history of the northern hemisphere 
is denoted. There is evidence of a gradual re- 
frigeration of the climate at the close of the Ter- 
tiary Age. This change of temperature, whicli 
effected the higher latitudes of the Old and New 
Worlds alike, reached such a height that the 
wliole of Northern Europe was buried under 
snow and ice, which extended southward as far as 
Saxony. The Alps and Pyrenees were loaded 
with vast snow fields, from which numerous gla- 
ciers descended into the plains, overriding ranges 
of minor hills on their way. The greater portion 
of Britain, and also a wide extent of North Amer 
ica, were wrapt in the cold embrace of huge ice 
fields. The effect of the movement of ice was 
necessarily to remove the soils and superficial 
deposits of the land surface. Hence in areas of 
country so affected, the ground having been 
scraped and smoothed, the glacial accumulations 
laid down upon them abruptly and without any 
connection with what was underlying them 
Considerable local differences maj' be observed in 
the nature and succession of the different deposits 
of the glacial period, as they are traced from dis- 
trict to district. It is hardly possible to deter- 
mine in some cases whether certain portions of 
the series are coeval or belong to different epochs. 
But the following are the leading facts which 
have been established for the North European 
area. First there was a gradual increase of cold, 
though with warm intervals, until the condition 
of modern North Greenland extended as far as 
Middlesex, Wales, the southwest of Ireland, and 
to 50° latitude in Central Europe. Tliis was the 
culmination of the glacial period. Tlien followed 
a considerable depression of land, and tlie spread 
of cold Arctic water over the submerged tracts, 
with abundant floating ice. Next came a re-eleva- 
tion with renewed augmentation of the snow fields 
and glaciers. Very gradually, and after intervals 
of increase and diminution, the ice retired toward 
the north, and with it the Arctic flora and fauna 
that had occupied the European plains. The ex- 
isting snow fields and glaciers of the Pyrenees, 
Switzerland, and Norway are remnants of the 
great ice sheets of the glacial period, while the 
Arctic plants of the mountains are relics of the 
northern vegetation which was universal from 
Norway to Spain. 
Nature and Origin of Glaciers. — A glacier may 
be defined .as a river of ice formed by the slow 
movement and compression of the snow which by 
gravitation creeps downward into a valley or 
plain descending from a snow field. From a geo- 
logical point of view these ice rivers may be re- 
garded as the drainage of the snowfall above the 
snow line, as rivers are the drainage of rainfall. 
In a mountainous region like the Alps, or table- 
land like Scandinavia, where a considerable mass 
of ground lies above the snow line, three varieties 
of glaciers have been observed : 
(a) Glaciers of the first order, where the ice 
river comes down well below the snow, and ex- 
tends into the valley, even ; it may be far below 
the upper limits of cultivation, and in northern 
regions approaches or even reaches the sea. In 
the Alps such glaciers may be twenty or thirty 
miles long by a mile or more wide, and six hun- 
dred or more feet deep. 
(6) Glaciers of the second order, which hardly 
creep beyond the high recesses wherein they are 
formed, and do not, therefore, reach as far as the 
next valley. Many striking and beautiful ex- 
amples of this type may be seen along the steep 
declivities which intervene between the snow-cov- 
ered plateau of Arctic Norway and the sea. 
(c) Kecemented glaciers, consisting of frag- 
ments which fall from an ice cliff" crowning preci- 
pice downwards, as glaciers of the second order 
usually do. Probably the best illustration in Eu- 
rope is furnished in the Nus Fyord and other parts 
of Northern Norway. In some cases a cliff" of 
blue ice appears at the top of the precipice, the 
same as at the edge of tlie great " snce-fond," or 
snow field, while several hundred feet below, in 
the come at the bottom, lies the recemented gla- 
cier, {glacier remanie of the Swiss), white at its 
upper edge. But it is in the high Arctic, and still 
more in the Antarctic, that land ice from the 
drainage of a great snow field attains its greatest 
dimensions. 
The land in these regions is completely buried 
under an ice cap whicli ranges in thickness — in the 
south polar circle 10,000 feet, (nearly two miles), 
and even more. Greenland lies under such a pall 
of snow that all its inequalities, save tlie more 
steep mountain peaks, are concealed, the snow 
creeping down the slopes and mounting over 
minor hills, passing beneath the pressure into 
compact ice. From the main valley great gla- 
ciers, like huge tongues, 2,000 or 3,000 feet thick, 
and sometimes fifty or more miles in breadth, 
push out to sea, where they break up into pieces 
ai.d float as icebergs. A glacier, like a river, is 
always in motion, though so slowly that it seems 
solid and stationary. The motion, also, like tliat 
of a river, and for the same reason, is unequal in 
its parts, the center moving faster than the sides 
and bottom. 'J'his important fact was first ascer- 
tained through accurate measurement by J. IJ. 
Forbes, who found that in the Mer de Glace of 
Chamouni the main daily rate of motion in the 
summer and autumn was from twenty to twenty- 
seven inches in the center, and from thirteen to 
nineteen and a half inches near the side. The 
consequence of this dlfTerential motion is seen in 
the arrangement of the lines of rubbish thrown 
down at the end of a glacier, which often present 
a horse-shoe shape, corresponding to tliat of the 
end of the ice by which they were discharged. 
According to the changed atmospheric relations 
the glaciers move now forward, then again back- 
ward, and their existence and extension is es- 
pecially proved by the following facts : 
Ice-worn or Erratic Backs. — We find solid rocks 
over the whole of Northern Europe which present 
the characteristic smoothly formed outlines which 
can be produced only by the grinding action of 
laud ice. Tliese outlines or erosions were effected 
not by the mere contact and pressure of the ice 
upon the rocks, though undoubtedly fragments of 
rock must now and tlien be detached from this 
