﻿524; ME. E. G. CAEEUTHEES ON" THE [Nov. ICJIO, 



be identified elsewhere, and may then yield a large number of 

 specimens. Accordingly, by spreading the investigation over a 

 wide area, a considerable amount of data has been got together. 

 In the end, the evolution of the gens has proved to be so slow and 

 gradual, tbat the separation of the various fossiliferous horizons by 

 considerable vertical intervals of barren strata has offered no 

 material check to the completion of the chain of evidence. 



II. Sequence of the Steata. 



It is as well to preface an account of the palssontological results 

 by briefly noting the general stratigraphical succession (see general 

 section, fig. 1, PI. XXXYI). 



The Lower Carboniferous rocks of Scotland, when fully developed, 

 show a conformable passage from the Upper Old Red Sandstone. 

 The lower two-thirds of the whole sequence is occupied by Calci- 

 ferous Sandstone strata, composed of a Cementstone Group, 

 succeeded, in the East of Scotland, by the Oil-Shale Group, or, along 

 the English Border, by the Fells Sandstone, and the Lawston coals 

 and limestones. Throughout the Central Valley corals are absent 

 in this great Calciferous Sandstone Series, excepting in the upper- 

 most beds. Near the Border, however, the Cementstones become 

 more distinctly marine, and not infrequently contain brachiopods, 

 polyzoa, etc., and occasionally small corals. The Lawston Lime- 

 stones l are thoroughly marine, although the variety of species or 

 genera which they yield is not great. 



Above the Calciferous Sandstone comes the Carboniferous Lime- 

 stone Series, divided into (1) the Lower Limestone Group, (2) the 

 Coal & Ironstone Group, and (3) the Upper Limestone Group. The 

 limestones in (1) and (3) occur in thin beds, separated by sand- 

 stones and shales, and most of them are of purely marine origin, 

 with abundant fossils. Marine bands are extremely rare in the 

 intervening Coal & Ironstone Group (2). 



This tripartite division of the Carboniferous Limestone Series 

 holds good throughout the country. The presence of a group of 

 workable coals between the two Limestone Groups is of incalculable 

 value to the stratigrapher, for it has given rise to extensive mineral 

 prospecting, by means of which individual beds of limestone can 

 frequently be traced for scores of miles. So much attention has 

 been paid to the Series in the Central Valley of Scotland, that in 

 this part of the country the horizon of any fossil locality can usually 

 be given within narrow limits. 



The upper limit of the whole succession may be said to be reached 

 at the abrupt break in the Carboniferous flora, which has been 

 shown by Dr. Kidston to take place about one-third of the way up 

 in the Millstone Grit (Eoslin Sandstone of the East of Scotland). 



1 By this term are indicated the two limestones, separated by a group of thin 

 coals, which appear in Liddesdale above the Fells Sandstone ; the upper bed is 

 known as the Lawston Linn Limestone. 



