04 
' THE MEDITERRANEAN NATURALIST 
natives go but little to the wooded hills behind, 
where the temperature goes down sometimes to 
15°. 5. cen. or lower, even on the hottest days. 
Mules bring down snow mightly in summer from 
covered pits in the hills, to supply the restau- 
rants and hotels. As to rain, there is a sharp con- 
trast between the wet winter half, and the dry 
summer half of the year. The registered rainfall 
shows (3-J inches) for the latter against 36 inches 
for the former. 
The autumn rains are ushered in by severe 
thunderstorms. November, and December are the 
wettest months, but about Christmas there is 
usually a short spell of fine weather. March is 
extremely variable, and often very wet. With 
May begin the rainless months, and the drought 
sometimes lasts considerably over a hundred days. 
Five months have sometimes passed with but a 
slight shower. Snow seldom falls in Angostoli, 
but it often falls on the hills. Dew is plentiful in 
summer, and is often very injurious to the crops 
owing to the salt precipitate that it forms. Wind 
is greatest in winter, southerly and southeasterly 
winds especially prevailing. A hot south-wind 
(the lambaditta) blows in the early summer, and it 
has a prejudicial effect upon the vegetation. The 
fresh north-east wind (the maestro) is the most 
invigorating, and it is usually accompanied by 
dense masses of cumulus cloud which clothe the 
the hilis around. 
T. M. 
Theories of Mountain Formation. 
By T. Millard Reade, C.E., F.G.S., F.R.I.B.A. 
Part II. 
THE first requirements of a geological theory 
are that it should conform to, and explain observ- 
ations made in the field. 
No speculations, however ingenious, are of much 
value in a geological sense if only deductively ar- 
rived at . hence a first requisite in the elaboration 
of a true theory of the origin of mountain ranges 
is an intimate knowledge of their geological 
structure. 
The careful observations of eminent geologists 
over the accessible portions of the known world 
go to prove that the universal characteristic of 
mountain ranges is the enormous thickness of the 
sedimentary deposits of which they are composed. 
This fact was first brought prominently forward 
in connection with the Appalachian chain by Prof. 
James Hall, of New York; and it is no less true of 
the Rocky Mountains, the Andes, the Alps, and 
the Caucasian, Himalaya, and Ural Mountains. 
Of these, we possess the most knowledge of the 
Alps and Appalachians, the combined thickness of 
the various formations of which they are severally 
composed being estimated by competent geologists 
at from eight to ten miles. It is a true generalisa- 
tion that the necessary preliminary to mountain 
building is great previous sedimentation. This, as 
all know who are at all acquainted with the 
principles of geology, means the destruction of so 
much land elsewhere, combined usually with the 
accretions from volcanoes either in the form of 
ashes or lava streams, or both. It is also none the 
less evident to the student of geology that this, 
again, means the lapse of enormous periods of geo- 
logical time. 
When we come to consider in what way these 
various strata are arranged in mountain chains, 
we find, as a universal fact which there is no gain- 
saying, that strata which have been aqueously laid 
down in approximately horizontal positions are in 
the regions of mountain ranges thrown into folds, 
and sometimes bent, contorted, and twisted into 
the most extraordinary convolutions. 
The one opinion novr held by geologists and 
physicists is, that these effects are mainly due to 
lateral pressure, but, as I have already showm 
much difference of opinion exists as to the origin 
of this pressure. Not only are soiid rocks folded 
into loops, but as a general rule — to which there 
are only a few exceptions known, and these I 
think are more apparent than real— there is in each 
great range a cential core composed of gneissic 
and granitic rocks, which often expands towards 
the summit, throwing the sedimentary beds 
through more than a right angle, producing an 
actual inversion of the strata, and what is called 
in geological parlance, “fan structure.” It is rocks 
of this nature that at present are, and for some 
years past have been, the subject of much interest- 
ing study and controversy. 
The age and origin of these foundation rocks are 
not by any means yet settled, but whether com- 
posed of metamorphosed sediments, or whether 
they are volcanic complexes altered and made 
