230 Professor Sedgwick and Mr. Murchison on the 



structure, and included organic remains, is recognized by all observers as the repre- 

 sentative of the carboniferous or mountain limestone of English geologists*. At 

 Cromford this rock is fully laid open in deep quarries, in which, after the incohe- 

 rent superficial deposits which cover so large a portion of this country have been 

 cleared away, we see the strata dipping to the N.N.W. at a high angle ; the ends 

 of the beds having been truncated and reduced to a plane surface, over which the 

 drift has been accumulated. The consideration of tertiary and detrital deposits forms 

 no part of our present inquiry ; but we cannot describe these quarries without 

 adverting to this remarkable appearance of the sharply-truncated edges of highly 

 inclined strata (the ends of which have been broken off and polished, as it were, 

 into an even pavement), and expressing our conviction that such a result could 

 not have been brought about without much violence, followed by powerful attrition 

 on the surface of the truncated strata, more particularly when we know that the 

 very same phaenomenon is exhibited on the surface of the older rocks under the 

 tertiary accumulations and drift in many parts of the borders of the Low Countries, 

 and in the northern provinces of Francef . 



When first cleared of the overlying drift, these ancient strata often convey the 

 false idea of being horizontally bedded, and their real position is only ascertained 

 by cutting into the body of the rock. 



The descending order of the strata of limestone at Cromford is as follows : — 



1. Shale and dark limestone, the thickness and relations of which are obscured. 



2. Great limestone, light grey, in beds from two to four feet in thickness : the lower beds fetid, faced 

 with carbonaceous shale, and in mineral aspect not unlike the great scar limestone of England. In this 

 mass are found most of the characteristic fossils, such as the Producta hemispherica, P. Comoides, 

 Encrinites, corals, and many of the species enumerated in our list. Dolomite occurs here and there in 

 irregular concretions throughout this rock, and is much used as a road-stone. 



3. Black shale, in parts calcareous, with corallines and Euomphali in the lower beds. 



4. Dark, hard limestone, used as a building and trough-stone, containing small spinose Productae, minute 

 Trilobites, &c. 



* See the sections and works of Hoffmann and of all preceding authorities. Our friend Von 

 Dechen has, in his last work, ' The Geological Map of Europe,' recognized the band of rocks which 

 immediately underlies the Westphalian coal-field as our millstone grit series, pointing out at the same 

 time the existence of the mountain limestone beneath it ; but he has merged the true mountain limestone 

 with another band which we shall show to be inferior to it. In short, although we consider the map of 

 Von Dechen to be of great value and generally very correct, our observations have convinced us, that, in 

 the eastern prolongation of the carboniferous limestone, there is an error, in consequence of which the 

 true equivalent of the lower coal series is not recognized in its extension over other parts of Westphalia 

 and the Rhenish provinces. 



t Striking examples of this powerful denudation, which smoothed and polished the inclined edges 

 of the mountain limestone, were long ago described by Messrs. Buckland and Conybeare in the Mendip 

 Hills (Geol. Trans., 2nd Series, vol. i. p. 225, PI. XXXV. fig. 2, 1824), and the same phenomena are to 

 be seen at Marquise, north of Boulogne. 



