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CARBONIFEROUS AND PERMIAN FORAMINIFERA. 



§ 2. GENERAL CONSIDERATIONS. 



That the Mountain Limestone rocks, which constitute so striking a geological feature 

 in the scenery of many parts of Great Britain, consist largely of chambered shells and 

 other microscopic organisms, which, until a few years ago, were spoken of collectively 

 under the indefinite term " Infusoria," is a belief that has probably existed ever since 

 men first wondered at the " fossil animalcules" in Chalk ; yet up to the present time 

 nothing has been written concerning the Rhizopoda of the Carboniferous age that has 

 any claim to be regarded as a history of the group. Perhaps, it is hardly too much to 

 say that the relation of the Foraminifera to the calcareous rocks of the Carboniferous 

 period has been assumed rather than studied ; and, as is commonly the case, views which 

 have gained currency under such circumstances are but partially substantiated by actual 

 observation. Take them as a whole, the Carboniferous Limestone beds of Great Britain 

 cannot be regarded as a microzoic formation in quite the sense in which the term 

 is rightly applied to many Cretaceous rocks : indeed, as a rule, they owe their origin, so 

 far as their organic constituents are concerned, much more to animals of higher 

 organization and larger individual dimensions, such as Crinoids and Corals, than to 

 Microzoa. As is well known, there are many important deposits of Secondary and 

 Tertiary age formed almost exclusively of the remains of Foraminifera, such as, for example, 

 the White Chalk of the South-east of England, the Nummulitic Limestones of Central 

 Europe, the Leythakalk of the Vienna Basin, and the Miliolite limestones of Hampshire 

 and elsewhere ; and a similar condition exists also in certain massive deposits of Car- 

 boniferous age, to wit, the white limestones of Russia, Central Asia, and North America ; 

 but in the Carboniferous rocks of our own country no portion of the vast series of beds 

 known in common parlance as " Mountain Limestone" has any claim to be placed in the 

 same category, except it be the comparatively inconsiderable section in which the very 

 simple form known as Saccammina is found. 



At first sight some of the microscopical sections of Carboniferous rocks represented 

 in the final plate of the present paper might lead to a different conclusion, but it must 

 be remembered that the specimens from which these figures were taken were selected for 

 the very reason that they contained unusual numbers of Foraminifera in a limited space — 

 the object being to illustrate the various aspects of the Foraminifera themselves, in situ, 

 rather than the general structure and composition of the rocks. It is very rarely indeed 

 that such a nest of minute forms as that shown in fig. 2 is to be found ; far more 

 frequently the field of an inch or an inch-and-a-half object-glass reveals but two or three 



