302 
THE MEDITERRANEAN NATURALIST 
represented by grey, and blue clays, spec imens of ] 
which may be observed in Beni Cliougrau. 
3. The Tortonian stage comprises a series of 
of argillaceous sands with Ancillaria giandifor- 
mis, mhos polygonum, Turritella vaj/riacensis 
and numerous varieties, Turritella Archimedis ■ 
Natica mille punctata , Nassa semistrata , etc., etc. i 
Above these the yellow sands and pebbles 
come next, and enter largely into the com- 
position of the hill of Chareb er Biha, and 
form the upper boundary of the Upper Miocene. 
IV. The general results are: — 
1. .The faunas of Mascara, and of Beni Bached 
and Carnot are identical. They do not belong 
to different stages, as has been published. 
2. The last elevation of the Atlas did not take 
place at the end of the Helvetian epoch (Middle 
Miocene) as has up to the present been believed. 
It is Post Tortonian and took place at the 
end of the Upper Miocene period, as the beds of 
Gontas, of Ben Chicas, of Teniet, and of Mascara 
are Tortonian. 
Poitiers. 
A ramble through. Emtahleb. 
Often when rambling through the rocky gorges 
and beneath the craggy escarpments of these is- 
lands, my attention has been drawn to the silent 
though effective manner in which the humblest 
agents in the economy of nature have their powers 
directed and husbanded, in order that the greatest 
effect might be produced with the least expendi- 
ture of energy. How many would imagine that the 
same plant life which clothes the hills, valleys, 
and plains on the islands’ surfaces, and which 
imparts such a charm to what would otherwise be 
all that is sterile and desolate, is one of the most 
unremitting of the many agencies that are at work 
in degrading down the rocks of which they are 
composed? 
Year after year it plays its part, unobtrusive- 
ly it is true, but so sure and- certain that as ages 
elapse the most stupendous changes are wrought 
in the contour of the islands’ surface. 
Measured by human experience, the changes are 
slow, and are but of little importance. The short 
spau of existence allotted to man i- nor sumeiei.t 
to allow him to appreciate their full significance, 
unless he can look back into the past and, using 
his own experience as an index can consider the 
aggregated changes that have been effected 
through the instrumentality of apparently such 
i insignificant causes. If he is prepared to do this 
i he may arrive not only at an approximation of the 
condition of things that formerly existed, but he 
may also obtain some idea of the nat - of those 
forces that are constantly engaged in the work c ; 
destruction. 
There is no spot in the two islands that will af- 
| ford more genuine pleasure to the lover of Nature 
| than will the charmingly situated valkq f Em- 
tahleb, with its rippling, purling streams and ver- 
dure-covered slopes; and . it will, a; the same 
time, afford more excellent opportunities for exa- 
mining closely the conditions under wki h the 
plant life of the caves and gorges exists, and the 
part it plays both in protecting and destroying the 
rock surfaces upon which it grows. 
Innumerable opportunities will present them- 
selves to enable one to observe the shifts to which 
the larger trees resort in their struggle Ur exist- 
ence. The rich though scanty soil that covers the 
slopes is not of sufficient depth to enable them, to 
obtain that hold in it that their great s:.:e de- 
mands, and they therefore insert their roots into 
the cracks and crevices of the strata and then, as 
in course of time, the increased bulk of the under- 
ground branches necessitates more space than the 
confined limits of the place will allow, the rock is 
shattered into fragments as effectively as though 
it had been subjected to the blows of a Brobding- 
nagian hammer. 
Descending the tortuous path wliich leads to 
the springs at the bottom of the valley, an esc dent 
example of the manner in which even a single tree 
may alter the physical aspect of the country in its 
immediate vicinity, is to be seen on the top of the 
cliffs that fringe it northern side. 
The gaunt, spectral trunk of an old earob tree 
overhangs the beetling brows of the rugged lime- 
stone cliffs, and seems to invite inquiry into the 
manner in which it has attained itsstrangeposition, 
