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PROCEEDINGS OF THE GEOLOGICAL SOCIETY. [Dec. 4, 



the north, denudation may probably have removed it. It is likely, 

 however, that at a comparatively recent geological epoch consider- 

 able changes have taken place amongst the Silurians of Dumfries- 

 shire, for we find several small isolated patches of the red sandstone 

 resting unconformably upon the former, the dip and position of 

 which would lead us to conclude that during the formation of that 

 deposit portions of the Silurians had been subjected to agencies 

 which modified their original contour, and which gave to the over- 

 lying sandstone its isolated character. 



3. Description of the Graptolites found in the Black Shales of 

 Dumfriesshire. By R. Harkness, Esq. 



[Communicated by J. C. Moore, Esq., Sec. G.S.] 

 [With a Plate.] 



The Graptolites occurring in Dumfriesshire present three well- 

 marked generic types : 1st. Those which consist of a single series of 

 cells, united together at the base, and also adhering along the sides 

 nearly to the orifice of each cell, — the cells being attached in an 

 oblique manner to the axis ; to these the name Graptolites is by 

 common consent applied, and they form the first section of that 

 genus, Monoprion, according to the arrangement proposed lately by 

 M. Barrande. 2nd. Those which have a foliaceous appearance, and 

 in which the cells are in two series, arranged along a central axis, — 

 features which characterize the genus Diplogr apsis of M'Coy*, and 

 the second section of Graptolites (Diprion) of Barrande. 3rd. Those 

 in, which the axis is reduced to a mere line, on which, at compara- 

 tively wide intervals, the cells are placed, and generally in a position 

 but slightly inclined. The complete isolation of the cells is the 

 distinguishing character of this genus, to which M. Barrande has 

 given the name of Rastrites. All these three forms occur in the 

 district under review. 



Concerning the nature of Graptolites and their relation to modern 

 species of zoophytes, it would appear from the general characters, 

 that the foliaceous species (section Diprion, Barrande) are not far 

 removed from the modern genera Pennatula and Virgularia. They 

 possess, in common with these, a solid central axis, which in some 

 cases is found extending much below the polype cells. A similar 

 axis also occurs in the two genera mentioned, and the mode of ar- 

 rangement of the cells in two series is also a common character. In 

 the case of some species of Diprion there is a difference in the form 



* At the Meeting of the British Association at Edinburgh, in July 1850, a list 

 was read, drawn up by Prof. M'Coy, of fourteen species of Graptolites from the 

 Silurian rocks of the south of Scotland. He has since kindly sent the plate in 

 which his new species are figured, and enabled us to identify two of them with 

 ours. It is thought that figures of the other species from this little-known district 

 will not be unacceptable. 



