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XLIY. 
0^ THE OCCUEEEI^CE OF SERPElS'TmE AT BRAY HEAD. 
By Peofessor J. P. O'EEILLY, Eoyal College of Science, 
Dublin. (Plate XXI.) 
[Read June 23, 1890.] 
In the Paper submitted to the Academy, January 28, 1889, On the 
directions of the lines of Jointing observable in the neighbourhood of 
the Bay of Dublin," the conclusion was arrived at, "that taking all 
the characteristics and conditions of the Eocks of Bray Head into 
consideration, there are strong reasons for questioning the purely sedi- 
mentary origin and nature which up to the present has been assigned 
to them (the Bray Head Eocks) by geologists." I further added: — 
" The reasons which have tended to force this view upon me may be 
classed under the two heads. Physical Characteristics and Chemical 
Composition" ; and I proposed to treat the question fully when making 
my Eeport on the results of the chemical analyses of the Bray Head 
Eocks for which grants of money had been given to me by the 
Academy. 
The continued examination of these Eocks, on the one hand, as 
well as the difficulty and delay attending the execution of a sufficient 
number of analyses to meet the requirements of the problem involved, 
have prevented the Eeport being brought to that state of completeness 
which I had hoped it to attain, and in which I am desirous of submit- 
ting it to the Academy. As a matter of fact, new observations are 
being continually made, and completeness of results seems hardly yet 
attainable. As, however, the subject of the present Paper may be 
treated separately, as it forms an excellent introduction to what I may 
have to say regarding the Bray Head Eocks taken as a whole, and as 
finally it brings out well the importance of chemical analyses for the 
determination of the true nature of this very remarkable series of 
beds, I have thought it advisable to submit the present Paper without 
further delay. 
The bed to which the following details refer has a history which it 
is desirable to record here. In the memoir to sheets 121 and 130 of 
the Geological Survey of Ireland, illustrating a portion of the counties 
