1914-15.] Chalk Boulders from Aberdeen, etc. 
287 
white limestone is commencing to be formed.” He believes “the most 
favourable locality for the formation of the sponge bed appears to be that 
one where currents are carrying only the very finest particles in sus- 
pension, the sediment on the ocean-fioor being almost purely calcareous.” 
In the case of these Scottish chalks we are dealing with submergence : 
the necessary conditions of sedimentation seem to have been fulfilled and 
sponge beds have resulted. They may, however, be representatives of the 
Lower Chalk, a view which finds support in the occurrence of an Holaster 
allied to Holaster loevis amongst the flint casts picked up at Cruden. 
Whether the Middle Chalk is represented and whether “ spheres ” have 
any value from a stratigraphical point of view is an interesting question. 
A 1, B 4, and B 10 very largely consist of these bodies, and in A 1 they 
are accompanied by Inoceramus fragments of similar character to those of 
the lower part of the Middle Chalk. In the South of England they are 
especially abundant at the base of the Middle Chalk, and this feature is 
persistent from Devon to Yorkshire. They cease to form an important 
part of the deposit in the Terebratulina zone, but come again with 
the Chalk Rock and occur commonly as high as the zone of M. cor- 
testudinarium. In Dorsetshire and Devonshire they are abundant in that 
zone. Above this, occurring sporadically, they cease to form an important 
integral part of the chalk, though with cells they continue to occur. It is 
possible that the three boulders above mentioned may be Middle Chalk or 
not higher than the zone of M. cor-testudinarium. 
The remaining boulders probably belong to the Upper Chalk ; two or 
three will compare in general character with the chalk represented in the 
flints. 
Desiring to compare the structure of the Belhelvie boulders with the 
Cretaceous rocks found in the west of Scotland, five thin sections and 
a hand specimen were courteously sent me by Professor W. W. Watts, at 
the kind request of Professor Judd, from the Royal College of Science, 
South Kensington ; and my friend Mr Jukes-Browne was able to send me a 
hand specimen and slides from the glauconite base and the siliceous chalk 
from Eigg, which had been kindly sent him by Mr Clough, as well as several 
slides of that found in Skye at Scalpay and Strollamus. The careful study 
of these much-altered chalks throws, unfortunately, but little light on those 
occurring in the north-east of Scotland ; this I very much regret, but in 
the absence of fossil evidence it would be mere speculation to attempt to 
correlate the siliceous chalk of the west with the boulders found at Belhelvie 
and off the northern coast of Aberdeenshire. 
Believing it possible that an examination of the Cretaceous rocks of 
