C. LAPW0RTH ON THE MOFFAT SERIES* 



323 



sarily an arbitrary one. It is drawn at the point where the first 

 bed of greywacke is seen in the section. 



Onr attention has been already directed to the peculiar seams of 

 white clay which form so striking a feature in the section of the beds of 

 this subdivision in the locality under description. They are nowhere 

 so remarkably conspicuous as at this spot, but they are never wholly 

 absent in any single exposure throughout the whole of the southern 

 portion of the Moffat district. 



It is clear from a comparison of the numerous sections of these 

 beds that the black bands increase in thickness and importance in 

 proportion as we pass across the district to the southward. To the 

 north they rapidly thin out, disappearing wholly in the sections 

 along the bands of Hartfell, Headshaw, Douglas, and Meggat. 

 There the grey beds form a single mass of barren rock, unrelieved 

 by any intercalated fossiliferous seam whatsoever. In this direction 

 they change gradually into a sheet of thin-bedded flagstone differing 

 in no way from similar beds clearly interbedded with the typical 

 greywackes of the Gala group. 



Hence it is highly probable that the line marking the summit of 

 the Moffat Series is actually drawn along slightly different horizons 

 in the different sections. Within the limits of the present district, 

 however, the error can be but slight, and its effect upon our conclu- 

 sions of no great moment. 



i. Zone of Diplograptus cometa. — This name is given to the first 

 eight feet of the Upper Birkhill Shales of Dobb's Linn. The lower 

 portion of the zone is formed of four feet of barren grey flagstone 

 (see fig. 29) ; the upper portion of a similar thickness of soft black 

 shales, weathering down into shivery fragments coated with the 

 oxide of iron. Lithologically the zone appertains to the Grey- 

 Shale group ; palseontologically its affinities are with the underlying 

 Black-Shale series. Its fossils are poorly preserved at this locality. 

 The only forms collected by myself are : — 



Rastrites capillaris (Carr.). 

 Monograptus lobiferus (M'Coy). 



leptotheca (Lapw.). 



cyplius (Lapw.). 



tenuis (Portl). 



— — Hisingeri (Carr.). 

 Diplograptus cometa (Gein.). 



Diplograptus tamariscus (Carr.). 



sinuatus (Nich.). 



folium (His.). 



Hughesi (Nich.). 



Climacograptus scalaris (His.), var. 

 normalis (Lapw.). 



The same bed appears to be exposed at Craigierig, Back Burn, in 

 the sections in the lower portion of Selcoth Burn below Craigmichan 

 Scaurs, &c. Beyond its value as a well-defined mineralogical horizon 

 in the section at Dobb's Linn, the zone is of very insignificant im- 

 portance in the Birkhill division. 



ii. Zone 0/ Monograptus spinigerus (Nich.). — Whatever misgivings 

 may be felt as to the propriety of erecting the B. -cometa band into a 

 distinct zone, not a moment's doubt can be entertained of the great 

 importance of the group of strata which immediately succeeds it. 

 Not only is its distinctness evident from the presence of several 



