374 CHARLES L. BOULENGER. 
by a desert ridge varying in width from one and a half to six 
miles. 
The Lake is connected with the Nile by means of the Bahr 
Yusuf; this is a canal about 200 miles long, which leaves the 
river near Assiut, and, passing through a break in the desert 
ridge, flows into the Fayfim where it divides into numerous 
branches, some of which discharge their superfluous water 
into the Birket el Qurun. 
At the present day Lake Qurun is situated about 150 miles 
to the south of the Mediterranean Sea; the Nile is a fast 
flowing river, and it is highly improbable that a medusa could 
have made its way upstream as far as the Fayiim; it is far 
more likely that Mcerisia is a relic of the sea, which in past 
times is known to have covered that part of Egypt in which 
the Lake is situated. 
The geology of Lower Egypt has fortunately been most 
carefully worked out in recent years, and on perusal of what 
has been written on the subject it is not difficult to imagine 
how this can have happened.} 
In early Pliocene times the valley of the Nile and the Red 
Sea were not yet in existence, and the Mediterranean covered 
the whole of Egypt to a little further south than Cairo. 
At a slightly later period violent dislocations took place in 
the position of the future Nile Valley, and a marine fjord was . 
formed in that district reaching as far south as the 24° of 
latitude. Into this fjord opened several rivers coming from 
the east over what is now the Arabian Desert, and there is 
no doubt that its waters were brackish. 
The Fayim depression was formed separately towards the 
same period, 1. e. late Plhocene, and was occupied by a large 
brackish lake connected with the Mediterranean on the one 
hand, and with the fjord of the Nile Valley on the other. It 
seems probable that at this time Moerisia, as well as 
' The following account of the geology of Hgypt has been compiled chiefly 
from the works of Beadnell and Blanckenhorn; references to these are given 
in the bibliography at the end of this paper. 
