1905-1906.] 
323 
also vastly simplified, resolving themselves chiefly into the 
transport of erratics as indications of the directions of ice-flows • 
t e presence or absence of marine organisms' remaining an 
important factor m differentiating between ice-sheets of inland 
and transmarine origin. 
Let us pass in imagination backwards over an unknown but 
vast number of centuries to a period when Arctic conditions 
p e vailed over Northern Europe, and mighty confluent fields of 
ice slowly travelled onward, traversing the North Channel, the 
yde, and the Irish Sea, grinding out deep troughs in the sea 
floor where such an obstacle as Rathlin Island obstructed the 
lower layers, enveloping it, Ailsa Craig, and the Isle of Man, 
overflowing eastward into England, and entering Ireland west- 
ward over the noble promontory of Fair Head, the first in our 
list of localities recorded in this summary. 
The iceworn summit of Fair Head is strewn with erratics 
rom many points of the compass, and strolling further south 
we observe many large blocks resting on the cliffs that encircle 
urlough Bay Noticing one of schist we ponder on its origin. 
Was it torn from a bed of similar rock on the shore many 
hundred feet below, or was it borne on ice ao miles across the 
over TtTr r r r! CS “ Cantyre ’ wh ° Se fra g men t* are shattered 
either d Glancing at the tiny handful of pebbles 
g thered at random, over Fair Head, which include a. small 
rounded fragment of Ailsa Craig, which lies due east, one from 
a point near Torr Head to the S.E., a bit of chert, old red 
cong omerate, and a peculiar smooth-looking green felsite from 
Scotland or North Antrim, we see the significance of studying 
the distribution of erratics and the important deductions to be 
drawn from their presence on these Ballycastle headlands 
Our summary includes 36 localities, and we will follow the 
course of the intrusive ice southwards, first considering the dis- 
tribution of erratics from Ailsa Craig which are much worn 
indrcating severe ice action, even some specimens dredged by 
Mr. Welch 40 fathoms deep off Rathlin were ground completely 
smooth. It occurred at 26 out of our 36 localities, has been 
found round our shores by Mr. Welch at Portrush in sandhills 
