204 



C. LAPWORTH Otf THE MOFFAT SERIES. 



cation between the various zones, and the included fossils are con- 

 sequently placed here in a single list. 



Monograptus gregarius (Lapw.). 



leptotheca (Lapw.). 



cyphus (Lapw.). 



tenuis (Portl.). 



communis (Lapw.). 



attenuatus (Hopk.). 



Diplograptus vesiculosus (Nich.). 



folium (His.). 



acuminatus (Nich.). 



modestus (Lapw.). 



tamariscus (Nich.). 



Climacograptus normalis (Lapw.). 



It will be apparent that here, as everywhere to the north of the 

 Garple Band, none of the Upper Birkhill fossils are present. 



Along the north-western margin of the ellipsoid the same Birkhill 

 Shales clearly constitute its marginal beds, passing below the suc- 

 ceeding flagstones and greywackes. 



In Billscleuch there is an exposure of these strata about half a mile 

 in length (fig. 22). They form two distinct subordinate anticlinals, 

 separated from each other by a narrow patch of greywacke. The 

 shales are perhaps less shattered than those in the Spa Score, but 

 are much more intensely altered. The lowest strata seen are cer- 

 tain pale shales coming into the place of the Barren Mudstone of 

 the sections to the south of the Moffat valley. Certain hard flaggy 

 beds which succeed probably represent the zones of D. vesiculosus 

 and M. gregarius. One band only is fossiliferous ; it contains Mono- 

 graptus cyphus (Lapw.) and Diplograptus tamariscus (Nich.). 



The grey flagstones and shales of the Upper Birkhill Shales cer- 

 tainly occupy much of the section between this unaltered band and 

 the greywackes. Beyond the fact that many of the highly altered 

 pale or cream-coloured beds show occasional seams of milk-white 

 mudstone no reliable evidence of their presence is obtainable. 



In Potburn, half a mile to the north-eastward, a similar group of 

 beds is visible. The strata are here less altered, and the majority 

 of the Lower Birkhill Graptolites are present. 



The shivery mudstone that everywhere underlies the greywackes 

 forms the extreme north-easterly point of the ellipsoid at the head of 

 Blackshope Burn, the surrounding cliffs showing the massive grit- 

 stone of the Gala group. In the very centre of the ellipsoid, midway 

 between the Spa Score and that of Billscleuch, a patch of greywacke 

 occurs on the ridge. Its northern margin is not exposed, but its 

 southern limit can be made out for about 200 yards above the cliffs 

 of the gorge. The grits dip to the southward at an angle of about 

 40° ; and there comes out from below them a band of grey shales 

 greatly indurated, representing the upper portion of the Birkhill 

 Shales. Along the south-western margin of this patch the pyritous 

 and flaggy black shales of the zones of M. gregarius and D. vesiculosus 

 are visible at the head of some small trough-like scores, and yield in- 

 differently preserved Graptolites of the characteristic species Mono- 

 graptus gregarius (Lapw.), M. tenuis (Portl.), Diplograptus tama- 

 riscus (Nich.), D. vesiculosus (Nich.). 



