360 
THE MEDITERRANEAN NATURALIST 
air would dart outward at more than a mile 
per second, and be lost in space; and as this 
would be repeated continually, ’such an atmos- 
phere could not be permanent on the moon. On 
the earth a copious atmosphere is retained for 
the reason that our globe is so ma-sive that 
a projectile could escape from its attraction only 
when given on initial velotcity of about six 
miles per second — a rate seldom or never reached 
by molecules of oxygen or nitrcgen. 
I N’ the sixteenth and seventeenth centuries, 
.navigators reported huge land tortoises in 
two widely separated regions— the Galapagos 
islands in the Pacific, and several islands in the 
Indian Ocean. The tortoises were taken from 
Mauritius and Reunion, but seen to ’have been 
particularly numerous in the smaller island of 
Rodriguez. From these islands they were in 1761 
being sent by thousands to Mauritius, but early 
in the century extermination was here complete 
and only in the little island of Aldabra are 
a few specimens of the tortoises now known to 
be living in a wild state. Steps are being taken 
to preserve these individuals, and to introduce 
them into other islands. Two tortoises — 2p feet 
high, with a shell 9i feet in circumference — 
are still living. 
A N extraordinary natural history has Madagas- 
car, declares Canon Tristram. One would sup- 
pose that this would be that of Africa, but it is so 
unlike as to prove that the island has been sepa- 
rated from Africa for an immense period of time. 
Its animals and plants, as well as its people, have 
a far greater resemblance to those of India than 
to those of the near mainland. The monkeys and 
lemurs of Madagascar are not to be found in 
Africa, while all the great African animals of prey 
are absent. Among the lemurs is one known as 
the ayeaye, the formation ..of whose digits is 
unique. The egg of an extinct bird of Madagascar 
is fifteen times the bulk of that of an ostrich, and 
yet the bird itself does not appear to have been 
larger than the New Zealand moa, an extinct bird 
to which it had an affinity. This same peculiarity 
runs through all the birds of Madagascar. The 
w'ater-birds and sea-fowl are of course those of 
Africa, but there are one or two extraordinary 
exceptions. The beautiful snakebird, allied to 
j the cormorant is an Indian, sj ecies. There is also 
a water-hen which is peculiar to Madagascar, and 
which has the remarkable features of a long tail 
and long foot. It is a great puzzle to naturalists. 
A group of cuckoos is peculiar to the island, with 
no relations in Africa or India; while a bird allied 
to the thrushes is not African but is allied to a 
species in the Mauritius and all the Mascarene 
islands. 
The Sandgate Landslip. (1) 
By W. Topley, F.R.S. 
The sea-front of the coast near Folkestone. 
Hythe, and Sandgate has long been known for its 
i tendency to slip, and ^numerous examples of land- 
slips, small and large, are there to be seen. In all 
these cases the cause of the slip is the geological 
structure of the ground, the strata consisting of 
alternations of pervious and of more or less im- 
pervious beds. At Eastwear Bay, between Folke- 
stone and Dover, there is a huge tumbled mass of 
chalk, known as “The Warren,” whi h has slinped 
over the impervious gault clay. As we proceed 
from east to west along the shore lower strata 
occupy the surface. Folkestone is mainly built on 
the highest division of rhe lower greensand— sands, 
sandstone, and hard calcareous bands, known as 
the Folkestone beds: these underlie the gault, and 
they overlie a set of clays and sandy clays known 
as the Sandgate beds. Where the latter beds crop 
out the old landslips begin, and they continue 
westward along the shore. The town of Sandgate 
is built on an old landslip of the Sandgate beds, 
and the recent slip is only a small movement in 
the old slip. West of Sandgate the Hythe beds rise 
from beneath the Sandgate beds. These arc bands 
of limestone and calcareous sandstone; they rest 
on Atherfield clay. The Atherfield clay, along its 
whole lngth for many miles to the west, has slipped 
more or less over the weald clay which underlies 
it, often bringing down masses of the overlying 
Hythe beds. 
Three miles to the west of Hythe are the 
remains of Studfall Castle, a Roman fortress built 
on the slope of the hill on Atherfield clay. This 
castle was destroyed by a landslip which probably 
(1) From the "Geographical Magazine' April 
1893 , 
