Hutt— On the Geological Age of the North Atlantic Ocean. 319, 
EXPLANATION OF PLATE VII. 
Fic. 1.—In this Map the areas of the Archean rocks, where they occur at the surface, are shown 
by the darker tint; and where these rocks may be inferred to pass underneath, and form the floor of 
newer formations, by the lighter tint or shading. It will be observed how large an area of both conti- 
nents is included. 
Fic. 2.—In this Map the areas of the Silurian rocks, where they occur at the surface, is shown by 
the darker colouring, and where they pass underneath, and form the floor of newer formations by lighter 
shade. These areas having been under the waters of the ocean in Silurian times, the approximate 
line of separation between the land and the sea is shown by the chain line. It is needless to observe 
that this line must have been constantly changing during the period ; but that indicated may be taken 
as the position towards the close of the Silurian epoch. 
