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SUPPLEMENT TO THE BRITISH 
Bracliiopods, writes me : " They appear to be found sparingly in tlie principal beds in 
which the large forms are met with, both in the Upper and Lower Limestones, but my 
experience is that, even when full-grown specimens are abundant, the minute ones are 
comparatively very rare. 
" The case, however, is completely reversed when we consider the upper thick ' post' of 
limestone belonging to the Lower Limestone series of Ayrshire. This bed, which attains a 
thickness of about forty feet, is made up almost exclusively of the exuviae of the marine 
fauna of the period, among which are the Brachiopoda. It is mostly a very white or 
cream-coloured limestone, and very pure in composition. It is acted upon by rain and 
other atmospheric agencies, which decompose it, and in washing, the greater part passes off 
as mud, leaving the shells (which appear to be composed of a more compact variety of hme- 
stone) and the hard fragments behind. Where this weathered limestone has been searched, 
minute Brachiopoda are found in abundance ; but of the five localities mentioned in list, 
where this bed is wrought, that of Dockra is the most worthy of note.^ Here the 
1 Mr. Robert Craig, of Langside, Beith, writes me : — " The words Lower Carboniferous Limestone 
are locally used in contradistinction to the Upper or Linn Limestone, 100 fathoms higher in the series above 
the lower coal and ironstones. This upper series, when preserved, is made up of a number of beds, generally 
of a lenticular character, not having a persistent thickness throughout. These beds of limestone are often 
one mass of the exuvise of marine fauna, the principal being the remains of Brachiopoda and Crinoidal 
stems. The remains of Productus are the most conspicuous, along with the stems of Crinoids. The 
horizon on which the small Brachiopoda at Dockra were obtained is about 12 feet from the upper surface 
or top of the beds, this amount of strata having been removed by erosion or denudation. At Trearne 
very little of the limestone was denuded where the fossils were found, so that the difference in the 
horizon in the two sections is about 10 feet. Therefore, if no other proof existed, it would be sufficient 
to show that they do not belong to one particular place in the beds ; but I have found them in other places 
below the upper surface of the Trearne bed, which proves them to be scattered through, at least, the upper 
20 feet of the series ; and I am of opinion that they extend throughout the whole. The Terebratulae are 
common to the whole ; in some places very abundant. If the small Terebratulse be the young of 
T. sacculus, it is rather curious to see them so abundant in this series of beds, while the old ones, or those 
full grown, are so moderately rare. In the Blue Limestone beds, sub-series of Beith, and in the Upper 
Limestone, Linn spout, Dairy, Terebratula sacculus and T. vesicularis are abundant ; but so far as I have 
observed the small ones are very rare and all but absent. The anomaly is this, that at Trearne and 
Dockra the full-grown specimens are rather rare and certainly diminutive, while in the sub-beds of the 
Lower Limestone and in the Upper Limestone full-grown specimens are not rare ; while the young 
found at Trearne are not found at Linn spout, Dairy, not more than one in a hundred. Younger and older 
specimens are found, but not like the small ones found at Trearne. I am not aware of any other 
beds in the locality where the small or minute Terebratulae are anything like in abundance, as they 
appear at Trearne. As they occur throughout the greater part of the beds you will perceive that they are 
associated with other shell remains common to the series, the principal and more common being Prod, 
longispinus and its varieties ; Prod, giganf.eus is always much crushed, it being very rare to find a good 
specimen. Prod, semireticidatus is not very common, but its varieties exceedingly so. The small variety 
sulcata is the most abundant, found both at Dockra and Trearne. Prod, punctatus common. Prod, 
spimdosus moderately abundant. Prod, mesoluhus and P , fimhriatus are rarer than any of the other Producti, 
Of Spirifers, Sp. dupUcicosta is the most abundant. Sp. trigonalis and its var. hisulcata, Sp. glabra, 
