atk. NA LUKRALLS® 
For 18993. 
NORWEGIAN BOULDERS IN HOLDERNESS. 
ALFRED HARKER, M.A., F.G.S. 
THE geologist whose lot is cast in East Yorkshire has no opportunity 
of examining igneous and crystalline rocks in place without making 
somewhat extended excursions. As a compensation for this, 
however, he has close to hand, in the boulders of the Holderness 
Boulder-Clays, specimens of many rocks of unique interest easily 
collected and studied. These are the spoils of the great Norwegian 
ice-sheet which, during the maximum glaciation of the region, 
crossed the North Sea, grounded in face of the chalk cliffs of 
Speeton, invaded the then bay of Holderness, and mingled its 
burden of foreign material with that brought by native ice from the 
English uplands. The boulders from Norway may be collected 
from the clays, especially the Basement-Clay of Dimlington and 
Bridlington, or from the beach south of Flamborough Head. They 
have been recorded by the officers of the Geological Survey, by 
Mr. Lamplugh and the present writer, and by various local workers. 
Many of them are of such characters as to be distinguished at 
a glance from all rocks of local origin, or from the igneous rocks 
transported from Teesdale, the Cheviots, or the Lake district. Two 
or three leading types are worthy of brief remark. 
(I.) Augite-Syenttes.—After the close of the Silurian period there 
were intruded among the Silurian strata of southern Norway a group 
of crystalline igneous rocks of peculiar types. Chemically they are 
remarkable for their richness in soda, and the mineralogical and 
structural characters of some of them distinguish them, in the eyes of 
the petrologist, from the rocks of all other districts. One marked 
type, largely developed in the coast-stretch between Christiania and 
Langesundstjord, is a variety of augite-syenite which Brogger has 
named /aurvikite, from the town Laurvig. Boulders of this rock are 
not difficult to find on the Holderness coast. It is rather coarsely 
crystalline, and presents a handsome appearance on a broken 
surface from the broad cleavage-faces of the felspars, the lustrous” 
black augite, and the occasional flakes of dark or golden-brown 
The felspars are often grey or dark in colour, and some- 
Jan, 1893. A 
