THE CARBONIFEROUS PERIOD. 



175 



that the marine fossils are in general derived from the inferior 

 portion of the system ; whilst the air-breathing, fresh-water, and 

 brackish-water forms are almost exclusively derived from the 

 superior portion of the same. 



The Carboniferous Protozoans consist mainly of Foramini- 

 fera and Sponges. The latter are still very insufficiently known, 

 but the former are very abundant, and belong to very varied 

 types. Thin slices of the limestones of the period, when ex- 

 amined by the microscope, very commonly exhibit the shells 

 of Foraminifera in greater or less plenty. Some limestones, 

 indeed, are made up of little else than these minute and elegant 

 shells, often belonging to types, such as the Textularians and 

 Rotalians, differing little or not at all from those now in exist- 

 ence. This is the case, for example, with the Carboniferous 

 Limestone of Spergen Hill in Indiana (fig. 114), which is 

 almost wholly made up of the spiral shells of a species of 

 Endothyra. In the same way, though to a less extent the 

 black Carboniferous marbles of Ireland, (and the similar mar 

 bles of Yorkshire, the limestones of the west of England and 

 of Derbyshire, and the great "Scar Limestones" of the north 

 of England, contain great numbers of Foraminiferous shells ; 

 whilst similar organisms commonly occur in the shale-beds 

 associated with the limestones throughout the Lower Carbon- 

 iferous series. One of the most interesting of the British Car- 

 boniferous forms is the Sac- 

 cammina of Mr. Henry Brady, 

 which is sometimes present in 

 considerable numbers in the 

 limestones of Northumberland, 

 Cumberland, and the west 

 of Scotland, and which is con- 

 spicuous for the comparatively 

 large size of its spheroidal or 

 pear-shaped shell (reaching 

 from an eighth to a fifth of an 

 inch in size). More widely dis- 

 tributed are the generally spin- 

 dle-shaped shells of Fusulina 

 (fig. 115), which occur in vast 

 numbers in the Carboniferous 

 Limestone of Russia, Arme- 

 nia, the Southern Alps, and 

 Spain, similar forms occurring in equal profusion in the higher 



Fig. 114. Transparent slice of Carbon- 

 iferous Limestone, from Spergen Hill, In- 

 diana, U. S., showing numerous shells of 

 Endothyra (Rotalia), Bailey I, slightly en- 

 larged. (Original.) 



