C. LAPWOB/IH ON THE MOEEAT SEEIES. 



313 



In Dobb's Linn the strata of the D. -Clingani zone visibly overlie the 

 streaked beds of the Climacograptus-Wilsoni zone in the southern 

 angle of the Main Cliff, but they are too much broken and meta- 

 morphosed to yield many fossils. The seam with Climacograptus 

 caudatus occurs in one of the small scaurs at the bottom of the cliff 

 near its centre, but is much more satisfactorily exposed in the 

 prolongation of the zone up the slope forming the angle between the 

 Long Burn and that descending from the falls. Some distance above 

 it occurs the well-marked seam with Dicellograptus caduceus, 

 swarming with its characteristic fossils, and traceable southward at 

 intervals in the Main Cliff, and northward over the summit of the 

 North Cliff, and thence through boi-.h the projecting bosses of hard 

 black flagstones in the slope beyond. 



All the fossils given in the list from Hartfell have been detected 

 In this zone in Dobb's Linn, together with the additional species : — 



Sipkonotreta rnicula (M'Coy). 

 Acrotreta Nicholsoni (Dav.). 



Lingula, sp. 

 Eurypterus, sp. 



In Glenkiln Burn a portion of this zone occupies the centre of 

 the synclinal of the Black Linn. The seam with Climacograptus 

 styloideus is easily detected on the north side of the trough, and, 

 higher up, the horizon of Dicellograptus caduceus. The prevalent 

 fossils appear to be : — 



Leptograptus flaccidus {Hall). 

 Amphigraptus radiatus (Lapw.). 

 Dicellograptus moffatensis (Carr.). 



Forchhammeri (Gein.). 



Dicranograptus ramosus (Hall). 

 Clingani (Carr.). 



Climacograptus caudatus (Lapw.), var. 



bicornis (Hall). 



Diplograptus foliaceus (Murch.). 

 Corynoides calycularis (Nick.). 

 curtus (La/pw.). 



Many of the same fossils are found in corresponding positions in 

 the zone as exposed at Mount Benger, Syart Score, Fall-Law Score, 

 Moory Syke, and Craigmichan. The last three localities also exhibit 

 its physical relationships to the zones above and below. 



iii. Zone of Pleurograptus linearis (Carr.). — The hard flaggy beds of 

 the D. -Clingani zone pass up everywhere by insensible gradations into 

 an overlying group of dark thin-bedded shales. In the lower 

 portions of this new group the shales split easily into thin slate-like 

 sheets, similar to those of the minority of the underlying beds. 

 Higher up they become thicker, softer, and tougher, while among 

 them appear thin seams and bands of barren shale, white or more 

 generally cream-coloured. These increase in number and import- 

 ance as we ascend, till, finally, they occupy the whole succession, 

 and pass insensibly into the great mass of barren mudstone of the 

 Upper Hartfell Group. Side by side with this change in the litho- 

 logical character of the strata, there takes j)lace a corresponding 

 alteration in the aspect of their included fossils. In the lowest 

 bands they are mere pyritous stains upon the surface of the laminae ; 

 in the highest they are frequently preserved in the round. 



The fossiliferous portion of the zone is best studied at Mount 

 Benger (fig. 16), where two longitudinal faults have isolated the 



Q. J. G. S. No. 134. y 



