492 Mr. Henslow’s Supplementary Observations to 
to reject his hypothesis, “that the existence of these concretions 
may be best accounted for by way of crystallization.” I can 
conceive no possible objection to their being considered embedded 
pebbles from the shores of the sea, any more than the marine 
exuviae, so prevalent throughout the limestone, to have been derived 
from the depths of it ; but, if we examine the facts presented, 
I think but little doubt can be entertained of their being the worn 
fragments of older rocks. 
In the first place, with the smaller nodules are mixed several 
pebbles, of large dimensions, whose structure is by no means 
crystalline, but granular; these again are associated with angular 
masses of quartz traversed by cotemporaneous veins of the same 
substance. The embedded materials when entering largely into 
the composition of any stratum appear pretty equally diffused, but 
when their number is comparatively small they occupy the lower 
portion, as if they had subsided from their greater specific gravity 
through matter in a liquid state. 
A similar aggregation takes place in the lowest stratum of the 
small patch of limestone which sets on to the south of Port-1 e- 
Murray, and if I recollect rightly at Cass-ny-Hawin also. 
Dr. Berger does not notice a change which sometimes takes 
place in the limestone, where its colour becomes reddish-brown and 
the texture crystalline. This appearance is slightly visible in 
Castletown bay, but occurs very plentifully to the south of Poolvash. 
Whether it forms a separate bed, in the latter case, or is merely a 
modification of the regularly stratified limestone is not so apparent. 
At one spot however, (marked c r r, in fig. 6, plate 35,) near the 
filack marble quarries at Poolvash, two or three eminences occur of 
this nature rising through the regular strata, which are wrapped 
round and abut against them in a very perspicuous manner, the 
