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VOL. XIV.(2) | THE PRESIDENT’S ADDRESS 89 
flags, shales and sandstones, with interbedded volcanic 
rocks here and there, and some limestones. 
The Bala Liméstone proper is not more than ten feet 
thick, so far as I have seen, but it seems probable that the 
thickness is irregular. The limestone is chiefly made up 
of fragments of shells, joints of Crinoids, valves of 
Ostracoda, and occasional portions of Polyzoa. In other 
Bala Limestones, apparently belonging to a higher horizon, 
the remains of Polyzoa are numerous and are regarded as 
the oldest known representatives of this class of organism. 
Mr Ruddy, of Bala, has made a most careful study of the 
Bala rocks, and has shown that in some sandstones and 
shales, fossil shells and Corals are numerous. He has 
also been successful in obtaining good specimens of 
Trilobites, some with eyes well preserved. Perhaps the 
most interesting of the Bala limestones is that of the 
Hirnant Pisolite, which seems to be a local deposit of 
about two feet thick, lying at the top of the Bala series in 
the Valley of Hirnant. It is especially interesting as 
being, so far as we know, the earliest form of oolitic 
structure. The process of formation was as follows :— 
Fragments of shell, Polyzoa, Crinoids, &c., settled on 
the floor of this early sea, and around these a crust 
formed, completely sealing them up in the form of a small 
granule, about half the size of a pea. To such an extent 
did this process go on that the feature of the limestone is, 
that it is chiefly made up of an accumulation of these 
granules. So well have the fragmental remains of the 
Polyzoa been preserved by this sealing-up process that the 
skeleton is sometimes perfect, even after this great lapse 
of time. An idea of this great lapse of time may be 
imagined when we remember that the great thickness 
of stratified rocks which form so important a part of the 
earth’s crust did not exist at the period that the Bala beds 
were deposited. 
