THE GEOLOGY OF SWITZERLAND. 
27 
if some is comparatively recent, at anyrate the 
oldest rock we know is Gneiss. This gives it a 
peculiar interest. The foliation of Gneiss is probably 
of two kinds: the one due to pressure, crushing, and 
shearing of an original igneous rock such as Granite, 
the other to original segregation-structure.* 
“Gneiss,” says Bonney, “may be, if not actually 
part of the primitive crust of the earth, masses ex- 
truded at a time when molten rock could be reached 
everywhere near to the surface.” ** When the crust 
of the earth first began to solidify the waters of the 
present ocean must have floated in the atmosphere 
as steam, so that even at the surface there would be 
a pressure equal to more than 1 2,000 feet of water. 
The cooling also must have been very slow. Still, 
the original crust, if we use the words in their 
popular sense to mean the superficial layers, was 
probably more like basalt, or the lavas of our exist- 
ing volcanoes. Gneiss, on the other hand, must have 
cooled and solidified under considerable pressure and 
at a great depth. When we stand on a bare surface 
of Gneiss we must remember — and it is interesting 
to recollect — that it must have been originally 
* Heim, Beitr. 3 . Geol. K. d. Sc/iw., L. XXIV.; Geikie, 
Text-book of Geology. 
** Story of our Planet. 
