254 C. LAPWOKTH OK THE MOFFAT SERIES. 



The strata referred to are, many of them, highly siliceous, and 

 weather down into small cuboidal fragments. Fossils are not 

 nncommon in the partings of soft black mudstones. The most 

 distinctive are Thamnograptus typus (Hall) and Didymograptus 

 super stes (Lapw.). 



It will be shown in the sequel that these beds appertain to a 

 third division of the Moffat Series. To this division I have given 

 the title of the Glenkiln Shales, from the spot where it yields its 

 characteristic fossils in the greatest abundance. 



Summary. 



Disregarding for the present the small patch of Glenkiln Shales 

 last described, it is evident that the strata of the Moffat series 

 exhibited in the Main Cliff of Dobb's Linn are naturally arranged 

 in two main divisions palseontologically distinct. Each of these 

 divisions, again, falls naturally into two well-defined mineralogical 

 subdivisions, each of which is, in turn, composed of several sub- 

 ordinate bands or zones, individually distinguishable by peculiar 

 lithological and palseontological features. Arranging the strata in 

 the order in which they are here displayed, and distinguishing each 

 band by its predominant or peculiar fossil, we have the succession 

 given in the following Table : — 



►3 / Upper Birkhill ] Zone of Bastrites maximus, Carr. 



g . or I Zone of Monograptus spinigerus, Mch. 



w | J Grey-Shale Group. J Subzone of Diplograptus cometa, Gein. 



Ma! Lower Birkhill "j Zone of Monograptus gregarius, Lapw. 



m m I or I Zone of Diplograptus vesiculosus, Mch. 



B I Black-Shale Group. J Zone of Diplograptus acuminatus, Mch. 



►**.«« I Zone of Dicellograptus anceps, Mch. 



I 2 ! -d„ Tv/r„i^„„„ n I Zone of " Barren Mudstone." 



P a 



Barren-Mudstone Group. 



Lower Hartfell \ Zone of Pleurograptus linearis, Carr. 



or I Zone of Dicranograptus Clingani, Carr. 



Black-Slate Group. j Zone of Climacograptus Wilsoni, Lapw. 



I. Glenkiln Shales. 



(b) Section along line A-B. (Plate XII. Sect. I.) 



With this provisional key to aid us, we proceed next to test 

 its accuracy by endeavouring to work out therewith the physical 

 arrangement of the Moffat Series of the main body of the glen. 



Returning to the lateral gorge beneath the falls, the section of the 

 North Cliff is resumed at the point where we left it, i. e. at the 

 north and south fault, by which the M.-gregarius zone of the Birkhill 

 Shales is brought into contact with the great band of barren mud- 

 stone. The North Cliff itself is divided into four distinct ridges by 

 three deep bays or " scores." The fault referred to runs up the 

 centre of the western score. Polio wing its direction carefully up 

 the face of the cliff, it is seen to cut the line of strike of the beds at 



