Edward A. Martin—“ How Long Ago” in Geology. 349 
Further, on examination of the Porth Gwichiaid Boulder-clay, as well, 
as that at Dulas Inlet, I found that the rest of its contents consisted 
of rocks foreign to Anglesey, with some of local Ordovician type, but 
that fragments from the Schistose Complex were rare or almost absent. 
The Schistose Complex cannot therefore extend to any distance beneath 
the sea to the north-east; indeed, the limit must coincide very nearly 
with the present coastline. 
Now, on reference to the sketch-map, it will be seen that the 
submarine curve we were considering runs as nearly as possible 
parallel to that of the coast itself as far as Point Lynas. To the east 
and north-east, therefore, it is clear that the existing land of Anglesey 
coincides very nearly with the limits of the old Crystalline and 
Ordovician Complex, and that the Irish Sea in that direction is floored. 
by Carboniferous and probably also by later rocks. 
Sketch-map of North-East Anglesey. The arrows indicate the direction of glaciation... 
Scale, two miles to an inch. 
IV.—‘‘ How Lone Aco” in Geotoey. 
By Epwarp A. Martin, F.G.S8. 
YQ: is frequently asked the question, how long ago is it since 
certain geological phenomena took place in which the questioner 
is interested for the time being. How long ago were the great 
coal-beds deposited, or how long ago is it since the chalk was formed 
at the bottom of the sea? 
