Vol. 56.] FORMATION AND ITS GRAPTOLITE-EAUNA. 447 



(3) Southern Scotland. — So far as is known at present the 

 Lower Ludlow Beds of Southern Scotland are non-graptolitic. 

 Monograptus colonus has, it is true, been recorded from the Biccar- 

 ton Beds, 1 and from the Pentland Hills at Habbie's Howe, 2 but its 

 identity with Barrande's M. colonus is as yet uncertain. 



(4) Dudley. — The Lower Ludlow Shales of the Midlands, inter- 

 vening between the Dudley and Sedgley Limestones, are not prolific 

 in graptolites. A few, however, have been obtained from time to 

 time by the workmen, and, through the kindness of Dr. Fraser of 

 Wolverhampton, I have been enabled to examine several specimens. 

 Only two species are recognizable : — namely, M. uncinatus var. 

 orbatus nov. and M. lioerneri; but both are exceptionally well pre- 

 served. The exact locality at which the specimens were collected 

 is unfortunately not known. 



Some good specimens of M. Roemeri from Dudley are in the 

 Natural History Museum, South Kensington. They probably came 

 from the beds overlying the Dudley Limestone, at one time grouped 

 popularly as Wenlock, but now known to be the representatives of 

 the Lower Ludlow. 



(5) The Abberley Hills. — Mr. Wickham King has sent me 

 several specimens of graptolites from the Lower Ludlow of the 

 Abberley Hills for identification : they are all typical Lower Ludlow 

 species. M. varians var. pumilus is abundant ; M. scanictis and 

 M. chimcera also occur. 



Y. General Summary. 



The Lower Ludlow Shales in Britain, when traced from one dis- 

 trict to another, exhibit many variations, not only in lithological 

 characters, but more especially in the thickness of their deposits. 

 Considered as a whole, the beds consist of calcareous mudstones 

 and flags, weathering to a characteristic light-brown ; but the 

 sediments become coarser and more arenaceous as they are traced 

 from the south and south-east to the west and north-west, and 

 whereas in the typical Ludlow district the whole thickness of 

 the Lower Ludlow (including the Aymestry Limestone) is only 

 about 1000 feet, in the Lake District it has apparently increased 

 to 10,000 feet. 



In spite of the marked variation in vertical extent, however, there 

 is a striking constancy in the sequence of lithological characters of 

 the sediments which distinguish the individual zones, at any rate in 

 the three districts which I have examined in most detail, namely 

 those of Ludlow, Builth, and the Long Mountain. Thus the zone 

 of M. vulgaris consists of hard flaggy shales, the zones of M. Nilssoni 

 and M. scanicus of softer and more shaly material, while that of 

 M. leintiuardinensis is made up for the most part of hard calcareous 



1 ' Scottish Monograptidae,' Geol. Mag. 1876, p. 505 & pi. xx, fig. 9. 



2 Mem. Geol. Surv. ' Silur. Rocks of Britain: vol. i, Scotland' (1899) p. 604. 



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