1122 The American Naturalist. [ December 
road, and scarcely enough for a narrow horse-path,. which is itself 
impassible at certain seasons of the year. The walls of the defile, 
which mainly consist of a compact dolomite limestone, and show the 
lines of stratification with unusual distinctness, rise almost perpen- 
dicularly into the air, and are altogether unscalable.’’ (Geol. Mag., 
Sept., 1891.) 
An Olenellus Zone in the Northwestern Highlands of 
Scotland.—At the last meeting of the British Association for the 
Advancement of Science, Sir Archibald Geikie read an important 
paper on the results of the geological survey work in Scotland. After 
referring to the various sedimentary formations which overlie the 
Lewisian gneiss, and the unsatisfactory evidence of the fossil remains 
in them as to their stratigraphical correlation, he described the dis- 
covery of a peculiar zone of blue or black shales which from their 
unaltered character promised to be fossil-bearing. This zone lies in 
what is known as the ‘‘ Fucoid beds’’ a few feet below the persistent 
band of ‘‘Serpulite grit.’ A search was at once begun, and resulted 
in the finding of undoubted fragments of Olenellus, More recently 
additional pieces of Olenellus, including a fine head-shield with eyes 
complete, have been found in another thin seam of black shale inter- 
leaved in the ‘‘Serpulite grit.’’ The finding of this fossil among the 
rocks of the Northwest Highlands, and its association with the ‘‘ Ser- 
pulite grit,” afford valuable materials for comparison with the oldest 
Paleozoic rocks of other regions. The ‘‘ Fucoid beds” and ‘‘ Ser- 
pulite grit,” which intervene between the quartzite below and the 
Durness limestone above, belong to the lowest part of the Cambrian 
system. The quartzites form the arenaceous base of that system, while 
the Durness may be Middle or Upper Cambrian. The marked uncon- 
formability which intervenes between the Torridon sandstone and the 
overlying quartzite points to a long interval having elapsed between 
the deposition of the two discordant formations.. The Torridon 
sandstone must therefore be pre-Cambrian. (Wature, Sept. 17th, 1891.) 
Origin of Petroleum.—lIn a recent paper Mr. Ross has endeav- 
ored to prove that petroleum is mainly generated by the action of 
solfataric volcanic energy upon beds of limestone, and gives equations 
to show that the action of sulphur dioxide and sulphurettcd hydrogen 
on carbonate of lime, with or without water and peroxide of hydrogen, 
is capable of producing the ethylene and marsh gas derivatives. 
(Nature, Sept. 17th, 1891.) 




