662 



ME. J. E. MAKE AND DE. H. A. KICHOLSOF 



conformity upon the limestone. One foot above the limestone is a 

 permanent divisional plane, -which is markedly slickensided, and along 

 which some movement has taken place. A little more than a foot 

 above this is another prominent, slickensided, divisional plane, against 

 which the laminae are seen to die out at the S.W. end of the cliff, 

 whilst at the X.E. end a little fault-breccia occurs, showing that 

 there has certainly been some disturbance here. About one foot 

 above this is a marked, pale-green band, and above this six feet six 

 inches of blackish shales occur, passing to the top of the cliff, where 

 a great mass of fault-breccia marks the position of a considerable 

 strike-fault. The Grraptolites preserved in these black shales, which 

 here have a thickness of at least 9 feet 9 inches, are difficult to ex- 

 tract from this cliff ; but fortunately at this point the shales are also 

 developed on the right bank of the stream, where the black calca- 

 reous shales are seen dipping immediately at those on the cliff, and 

 an examination of the rocks in the bed of the stream forbids the 

 existence of any fault. The identity of the beds is proved by the 

 fact that the Graptolites, which are beautifully preserved in the shales 

 seen in an excavation in the bank, a few feet above the stream, are 

 identical with those obtainable with some difficulty in the shales of 

 the cliff. These species are : — 



Monograptus leptotheca, La/gw. 



Sanderson!, Lapw. 



• revolutus, KurcJc. 



tenuis, Portl. 



attenuatus, IIoj)k. 



Dimorphograptus confertus, 



Nick. 

 elongatus, Lapw. 



Diplograptus sinuatus, Nich. 



longissimus, KurcJc. 



Tesiculosus, Nich. 



Climacograptus normalis, 



Lapw. 

 minutus, Carr. 



Of these forms the most noticeable are the remarkable Dimorpho- 

 graptus confertus.^ iN'ich., which occurs in swarms, especially along 

 one bedding-plane, where it is found to the almost complete exclusion 

 of any other species, and Monograptus revolutus, which is also very 

 abundant. One example of Dimorphograptus elongatus occurred. 



We shall speak of this zone as the Dimorphograptus-confertus Zone ; 

 and this and the underlying zone, we regard as constituting the 

 Loiver Shelgill Beds. 



It will be convenient to consider the development of these beds in 

 other parts of the gill before proceeding to describe the higher sub- 

 divisions. 



Although the Lower Bridge crosses the gill in the wooded portion, 

 nevertheless the wood mainly occupies the left bank of the stream 

 until we attain a point a few yards below the Lower Bridge, where the 

 right bank also becomes wooded, to the south-west of a wall which 

 runs down this bank to the top of the small cliff overhanging the 

 stream. Here the fault described as occurring at the top of the 

 small cliff in which the beds of the Dimorphograptus-confertus Zone 

 are developed has come down to the stream, and the Ashgill Shales 

 are immediately succeeded by higher beds, which are much crushed 



