194 COOKE : JACKSON AND VICKSBURG DEPOSITS 



been found in the Mint Spring marl. Twelve mollusks, 3 of 

 which range through the Vicksburg group, are listed also from 

 the Jackson formation, but some of these are characterless 

 species of supposedly very long range. 



MARIANNA LIMESTONE 



The name Marianna limestone was given by Matson and 

 Clapp^^ in 1909 to the soft, porous, light-gray to white limestones 

 at Marianna and other places in w^estern Florida ''which are 

 characterized by an abundance of Orhitoides mantelli and other 

 Foraminifera associated with many other fossils, prominent 

 among which are Pecten poulsoni and P. per planus. '"'^'^ The 

 last named species has since been found to be restricted to under- 

 lying Eocene strata^^ and was referred to the Marianna limestone 

 by mistake. 



The Marianna limestone was included in the Vicksburg group 

 by Matson and Clapp, by whom it was regarded as the strati- 

 graphic equivalent of the upper part of the bluff at Vicksburg 

 (Byram marl). It was later found to lie conformably upon the 

 Ocala limestone, 22 which had been thought to be the highest 

 formation of the Vicksburg group. 



The typical Marianna hmestone is very homogeneous, white 

 or cream-colored, and when first quarried is so soft that it is 

 easily sawed into building blocks which harden on exposure. 

 Because of its extensive use for building chimneys, it is popularly 

 known as "chimney rock." This facies of the Marianna lime- 

 stone extends with remarkable uniformity from Marianna, 

 Florida, nearly to Pearl River, Mississippi. It is characterized* 

 nearly everywhere by a great profusion of Bryozoa and an 

 abundance of Lepidocyclina mantelli, Pecten poulsoni, and 



"Matson, G. C, and Clapp, F. G., A preliminary report on the geology of 

 Florida: Second Ann. Rept. Florida Geol. Survey, p. 51. 1909. 



20 Idem, 52. 



2' Not having seen the type of Pecten perplanus, I am accepting as correct the 

 species so named in the collection of the U. S. National Museum and described 

 by Dr. Dall {Tertiary Fauna of Florida, p. 732). Hopkins has figured a specimen 

 on plate 27, in U. S. Geol. Survey Bull. 661-H. 



22 Cooke, C. W., The age of the Ocala limestone. U. S. Geol. Survey Prof. 

 Paper 95: 109. 1915. 



