SUBORDINATE GROUPS OR FORMATIONS. 129 



lowest member of the series, which, if developed and exposed in that 

 locality, would raise the aggregate to at least 16,000 feet. It is 

 certain, however, that the thickness is very variable, and that in some 

 districts particular members of the series are wanting, or are only 

 slenderly developed. Still the section at the Joggins is by no means 

 an exceptional one, since I have been obliged to assign to the Car- 

 boniferous deposits of Pictou, on the evidence of the sections exposed 

 in that district, a thickness of about 16,000 feet; and Mr R. Brown 

 of Sydney has estimated the Coal formation of Cape Breton, exclusive 

 of the Lower Carboniferous, at 10,000 feet in thickness. 



When fully developed, the whole Carboniferous series may be 

 arranged in the following subordinate groups or formations, the limits 

 of which are, however, in most cases not clearly defined : — 



(1.) The Upper Coal Formation, containing coal formation plants, 



but not productive coals. 

 (2.) The Middle Coal Formation, or coal formation proper, con- 

 taining the productive coal-beds. 

 (3.) The Millstone-grit Series, represented in Nova Scotia by red 

 and gray sandstone, shale, and conglomerate, with a few 

 fossil plants and thin coal seams, not productive. 

 (4.) The Carboniferous Limestone, with the associated sandstones, 

 marls, gypsum, etc., and holding marine fossils, recognised 

 by all palaeontologists who have examined them as carbon- 

 iferous. 

 (5.) The Lower Coal Measures, holding some, but not all, of the 

 fossils of the Middle Coal formation, and thin coals, not 

 productive ; but diflfering both in flora and faima from the 

 Upper Devonian, which they overlie unconformably. 

 In regard to their mineral character, thickness, organic remains, 

 and geographical distribution, these several formations may be de- 

 scribed as follows : — * 



(«.) The Upper Coal Formation. — Consists of sandstones, shales, 

 and conglomerates, with a few thin beds of limestone and coal. Cala- 

 mites Suckovii, Annularia galioides, Cordaites simplex, Alethopteris 

 nervosa, Pecopteris arborescens, Dadoxylon materiarium, LepidojMoios 

 parvus, and Sigillaria scutellata, are among its characteristic vegetable 

 fossils. Its thickness is 3000 feet or more ; and its shales and sand- 



* If tlie reader sliould, in glancing at these descriptions, or at the succeeding 

 sectional list, meet with technical terms not familiar to him, he will find their 

 explanation farther on, in the chapters and notes relating to Carboniferous fossils. 

 Descriptions of genera and species may be referred to by looking up their names in the 

 index, where the numbers of the pages in which they are described or figured will 

 be indicated. 



