GEOLOGY: C. SCHU CHERT 
71 
as we know it may, there seems no good reason why a basalt magma issuing 
into cold water on the sea-floor might not be similarly affected and have an 
upper glassy crust. Such a glassy skin on the lava would seem an even more 
natural result from the melt being plunged into cold water than if it cooled 
in the air, the pressure of the depth of water being a minor consideration 
compared with the sudden change of temperature. The experience of man- 
kind from remote ages has taught that the quickest and most convenient way 
of suddenly cooHng a heated material is to plunge it into cold water. 
That basaltic glasses, or tachylytes, are not formed solely under atmos- 
pheric conditions is shown also by the fact that they have been found as the 
selvage edges of intrusive rocks, in dikes, and in intrusive sheets, in Finland, 
Sweden, Connecticut, and elsewhere. These glassy sulbands are now re- 
vealed to us only after prolonged erosion, and the geologic evidence would 
appear to indicate that they were probably formed under greater pressures 
than would be produced by the weight of the water of the ocean. It was 
the sudden chilling, produced by the contact with cold rocks, which forced 
the glass to form in spite of the pressure. 
In the light of petrographic experience it does not seem that the generali- 
zation of Professor Termier is well founded. The fact of dredging glass 
splinters from oceanic depths in a volcanic region can hardly be held in it- 
self as a proof of profound subsidence of such an area from sub-aerial conditions 
The conclusions from these various studies are (1) that the Azores 
are volcanic islands and are not the remnants of a more or less large 
continental mass, for they are not composed of rocks seen on the con- 
tinents; (2) that the tachylytes dredged up from the Atlantic to the 
north of the Azores were in all probability formed where they are now, 
at the bottom of the ocean; and (3) that there are no known geologic 
data that prove or even help to prove the existence of Plato's Atlantis 
in historic times. 
The greater question, was Africa ever united to South America is 
being answered by biologists and geologists, 'yes' and 'no.' The writer, 
however, believes in this connection previous to the Tertiary and thinks 
that the down-breaking of western Gondwana began in the late Lower 
Cretaceous, with complete severance long before the close of Eocene 
time, for marine strata of this age are general along the western border 
of Africa. On the other hand, if this land bridge had continued unbroken 
into Tertiary time, even only as late as the later Eocene, then certainly 
the wonderful fossil mammalian faunas of Argentina should have re- 
vealed many and unmistakable African links. The African affinities 
in the ancient South American mammalian faunas are, however, so 
slight as to give but a very limited support to the theory that Gond- 
wana was still in existence in early Tertiary time, and none at all to 
