THE CARBONIFEROUS PERIOD. 171 



have been formed in inland swamps and morasses, or in brack- 

 ish-water lagoons, creeks, or estuaries. A corresponding dif- 

 ference exists necessarily in the animal remains of these de- 

 posits, and in many regions this difference is extremely well 

 marked and striking. The great marine limestones which 

 characterise the lower portion of the Carboniferous series in 

 Britam, Europe, and the eastern portion of America, and the 

 calcareous beds which are found high up in the Carboniferous 

 in the western States of America, may, and do, often contain 

 the remains of drifted plants ; but they are essentially charac- 

 terised by marine fossils; and, moreover, they can be demon- 

 strated by the microscope to be almost wholly composed of 

 the remains of animals which formerly inhabited the ocean. 

 On the other hand, the animal remains of the beds accompany- 

 ing the coal are typically the remains of air-breathing, terres- 

 trial, amphibious, or aerial animals, together with those which 

 inhabit fresh or brackish waters. Marine fossils may be found 

 in the Coal-measures, but they are invariably confined to spe- 

 cial horizons in the strata, and they indicate temporary depres- 

 sions of the land beneath the sea. Whilst the distinction here 

 mentioned is one which cannot fail to strike the observer, it is 

 convenient to consider the animal life of the Carboniferous as 

 a whole : and it is simply necessary, in so doing, to remember 

 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 P7'otozoans consist mainly of Foraijwii- 

 fera and Spotiges. 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 Foramifiifera 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 



