Ch. Xm.] t FOSSILS OF THE SUFFOLK CRAG. 203 



or 4 in breadth, between the rivers Aide and Stonr. It is generally 

 calcareous and marly — a mass of shells, bryozoa,* and small corals, 

 passing occasionally into a soft building stone. At Sudbourn, near 

 Orford, where it assumes this character, are large quarries, in which 

 the bottom of it has not been reached at the depth of 50 feet. At 

 some places in the neighborhood, the softer mass is divided by thin 

 flags of hard limestone, and bryozoa placed in the upright position in 

 which they grew. 



From the abundance of these bryozoa or coralloid mollusca the 

 lowest or "White Crag obtained its popular name ; but true corals, as 

 now defined, or zoantharia, are very rare in this formation. 



The distinctness of the fossils of the Coralline from those of the 

 Red Crag, arises in part from their higher antiquity, and, in some 

 degree, from a difference in the geographical conditions of the sub- 

 marine bottom. The prolific growth of echini, bryozoa, and a pro- 

 digious variety of testacea, implies a region of deeper and more tran- 

 quil water ; whereas, the Eed Crag may have been formed afterward 

 on the same spot, when the water was shallower. In the mean time 

 the climate became decidedly somewhat cooler, and some of the 

 zoophytes which flourished in the first period disappeared, so that the 

 fauna of the Red Crag acquired a character more nearly resembling 

 that of our northern seas, as is implied by the large development of 

 certain sections of the genera Fasus, Buccinum, Purpura, and Tro- 

 chus, proper to high latitudes, and which are wanting or feebly repre- 

 sented in the inferior crag. 



Some of the corals and bryozoa of the lower Crag of Suffolk belono- 

 to genera unknown in the living creation, and of a very peculiar struc- 

 ture ; as, for example, that represented in the figure (155) on the fol- 

 lowing page, which is one of several species having a globular form. 

 The great number and variety of these zoophytes probably indicate 

 an equable climate, free from intense cold in winter. On the other 

 hand, that the heat was never excessive is confirmed by the preva- 

 lence of northern forms among the testacea, such as the Ghjcimeris, 

 Cyprina, and Astarte. Of the genus last mentioned (see fig. 156) 

 there are about fourteen species, many of them being rich in indi- 

 viduals ; and there is an absence of genera peculiar to hot climates, 

 such as Conus, Oliva, Jlitra, Fasciolaria, CrassateUa, and others. 

 The cowries (Cyprvea, fig. 153), also, are small, and belong to a sec- 

 tion (Trivia) now inhabiting the colder regions. A large volute, 



T Ehrenberg proposed in 1831 the term Bryozown, or "Moss-animal," for the 

 molluscous or ascidian form of polyp, characterized by having two openings to the 

 digestive sack, as in Eschar a, Flustra, Retepora, and other zoophytes popularly 

 included in the corals, but now classed by naturalists as mollusca. The term Poly- 

 sown, synonymous with Bryozoum, was, it seems, proposed in 1830, or the year 

 before, by Mr. J. V. Thompson, but is less generally adopted. The animals of the 

 Zoantharia of Milne Edwards and Haime, or the true corals, have only one opening 

 to the stomach 



