312 



C. LAPWOPvTH ON THE MOFFAT SERIES. 



arbitrary line is chosen, where the grey ribs and pale seams of the 

 C- Wilsoni zone disappear. Above, it is conveniently limited by 

 the horizon in which Pleurograptus linearis (Carr.) and its associates 

 are first detected. 



At no single locality within the limits of the Moffat district are 

 the beds of the zone in such a condition as to admit of individual 

 study and admeasurement. Nevertheless it is generally possible to 

 make out the various horizons, and to arrive at a close approxi- 

 mation to the true thickness of the entire zone. 



At Hartfell its total thickness is about 22 feet, as measured 

 among the broken beds above the line of the 0.- Wilsoni zone in the 

 " cornice " in the northern slope of the gorge. In Dobb's Linn 

 24 feet may perhaps be assigned to it. In the greatly shattered 

 sections in the other localities mentioned it is impossible to estimate 

 its original thickness. 



Palseontologically, the most remarkable characteristic of this zone 

 is the fact that fossils are totally absent from many of the beds and 

 are strictly confined to certain horizons, the strata of which do not 

 differ in any appreciable degree from those of the barren beds. On 

 each of these horizons there is found usually a single species or 

 variety, its individuals lying scattered all over the face of the 

 stratum in countless numbers and in the wildest confusion. 



At Hartfell three of these horizons are especially conspicuous. 

 The lowest is characterized by the exclusive presence of Climaco- 

 graptus cauclatus. It lies about 4 feet above the base of the zone, 

 and recurs again and again in the numerous convolutions of the 

 northern cliffs. The second swarms with Dicellograptus caduceus 

 (Lapw.), and is found near the centre of the zone ; but as it is 

 restricted to a few inches of the succession it is less easy of recog- 

 nition. The third includes several neighbouring strata near the 

 summit of the zone. Its peculiar fossil is Climacograptus styloideus 

 (Lapw.), which may be collected in abundance at several points in 

 the North Cliff. 



The foregoing are peculiar forms, wholly unknown outside the 

 limits of the horizons they distinguish ; but there are numerous 

 additional horizons belonging to such long-lived forms as Dicello- 

 graptus Forchliammeri (Grein.), D. Morrisi (Hopk.), Betiolites fibratus 

 (Lapw.), &c. &c. 



The species occurring within the limits of this zone in the typical 

 section of Hartfell include : — 



Leptograptus flaccidus {Hall). 

 Amphigraptus radiatus {Lapw.). 

 Dicellograptus Forchhammeri {Grein.). 



moffatensis {Carr.). 



caduceus {Lapw.). 



Dicranograptus ramosus {Hall). 



Nicholsoni {Hopk.). 



Clingani {Carr.). 



Climacograptus bicornis {Hall). 



scalaris {His.). 



, var. caudatus {Lapw.). 



Climacograptus scalaris, var. styloideus 



{Lapw.). 

 Diplograptus foliaceus {Murch.). 



truncatus {Lapw.). 



tricornis {Carr.). 



Lasiograptus margaritatus {Lapw.). 

 Retiolites fibratus {Lapw.). 

 Lingula, sp. 

 Corynoides calycularis {Nich.). 



curtus {Lapw.). 



Eurypterus, sp. 



