488 Mr. W. W. Stoddart on a, Mkrosoal Bed 



lowest calculation, 20 per cent, of the entire rock. From one 

 avoirdupois pound of the rock the author obtained 1,600,000 

 distinct and perfect fossils, besides a large quantity of broken 

 shells and other debris. Indeed the whole bed may truly be 

 said to be composed of an immense mass of Microzoa united 

 together by a crystalline calcareous cement. 



The most remarkable feature is that, although the fossils are 

 of genera that are usually found of a tolerably large size, and 

 are so found in the superincumbent beds of the shales, yet here 

 they are species so minute that they average from T <j^ inch to 

 2^ inch in diameter. When separated from the limestone, their 

 appearance is exactly that of having been sifted through a fine 

 sieve. 



This extraordinary deposit was evidently a submarine bank 

 in the Carboniferous Sea, exposed to currents which would wash 

 away the larger shells and zoophytes, from their offering a 

 greater resistance to the water. The smaller organisms would 

 be left as a deposit in the hollows or adhering to the ground, 

 forming a smooth floor, over which the water could flow with 

 unimpeded velocity. 



Many instances of this action are now occurring on our own 

 coasts. On the west side of Caldy Island is a sand-bank most 

 singularly analogous to that of the limestone-bed in its contents. 

 There the author collected a very numerous series of small shells 

 which (with the exception, of course, of the Encrinites) very 

 closely resembled the contents of the Bryozoa-bed both in 

 numbers and size. Among others were small Turritellce, Cythe- 

 ridce, young Trochi ; and, what made the analogy more striking 

 still, the only zoophytes were the Salicornariee, which lay strewed 

 about in great abundance, broken into joints exactly resembling 

 the Carboniferous Ceriopora. Very probably, therefore, the 

 Bryozoa-bed was once a bank similarly situated, and exposed to 

 the same influences as this and many others that are equally well 

 known. The Encrinites must, however, have been a very small 

 species, from the perisomic plates being so diminutive. This 

 fact alone would negative the supposition of some, that the re- 

 mains may be those of the arms only, the larger columnar por- 

 tions being washed away. The structure also precludes that 

 idea, as the ossicula are those of the columnar as well as the 

 brachial apparatus. 



Very many more species of fossils occur than those given in 

 the engraving (PI. XVIII.), they being those most commonly met 

 with. They are represented as they appeared with a power of 

 60 diameters, and sketched by means of a camera lucida. The 

 measurements were taken in the usual way with an eye-piece 

 micrometer. 



