ON THE VERTICAL MOVEMENTS OF THE ATMOSPHERE. 165 
‘ From Dungloe, as head-quarters, the structure of Crohy Head was carefully 
examined, and also the island of Arranmore, which differs materially in its 
structure from the mainland of Ireland, from which it is only distant three 
miles. The southern portion of this island is nearly entirely composed of 
white granite, penetrated by numerous dykes of syenite and of felspathic 
porphyry. The strike of these rocks is nearly E. and W., while that of the 
flagey quartz-rocks on the northern shore of the island approaches N. and S. 
During the course of this tour, two more sections were made across the 
granite of the main axis, exhibiting the same facts which had been observed 
before, viz. numerous beds of limestone and of altered slate lying in the 
granite, stratified nearly conformably with it. These were observed in the 
centre of Glenveagh, close to Ballaghgeeha Gap, on the pass through the 
Poisoned Glen from Dunlewy. At Glenleheen, where the same occurrence 
of non-granitic rocks had been observed in the previous year, four beds of 
limestone and several beds of slate were discovered. Almost all these beds 
of limestone contained garnet, idocrase, and epidote in quantity ; and at Glen- 
leheen itself, scapolite, a mineral whose occurrence in the British Islands has 
escaped the notice of modern English mineralogists, was discovered. Inas- 
much as the specimens brought home by the members of the Committee 
from their several tours are very numerous, it is not possible for them to 
present their complete report at this Meeting. They hope to embody in it 
some valuable information relating to the granitic rocks of Canada, which 
Dr. T. Sterry Hunt has kindly offered to supply to them. They have to 
express their thanks to him and to Mr. Harte, C.E., county surveyor of the 
western district of the county, who, with the Rev. Frederick Corfield, has 
afforded them most efficient assistance. They have succeeded in procuring 
some of the granite of Rockall, through the kindness of the officers of H.M.S. 
Porcupine, who furnished it to Mr. Harte, and wil] include its analysis in 
their paper. 
On the Vertical Movements of the Atmosphere considered in connexion 
with Storms and Changes of Weather. By Hunry Hennessy, 
F.RS., M.R1IA., &c., Professor of Natural Philosophy in the 
Catholic University of Ireland. 
Tue labours of the Committee, consisting of Admiral FitzRoy, Mr. Glaisher, 
and myself, who were appointed, at Manchester, for the purpose of studying 
the vertical disturbances of the atmosphere with the aid of instruments, 
have, for the present, been restricted to the work of a single observer. This 
has arisen from the circumstance that the money-grant appropriated to the 
Committee has sufficed only to defray the cost of erecting a single instrument. 
As this instrument is likely to afford opportunities for observing the vertical 
motions of the atmosphere more completely than has been hitherto possible, 
it is to be hoped that similar apparatus will before long be in the hands of 
the other members of the Committee. The fact that all the preliminary work 
has thus necessarily devolved on the writer of the present Report will suffi- 
ciently account also for its provisional nature. 
Hitherto the only kind of atmospherical currents which have formed the 
subjects of definite observation by instruments are those whose existence is 
manifested by the movements of ordinary wind-vanes and anemometers. 
But as these instruments indicate horizontal movements exclusively, ordinary 
