C. LAPW0RTH ON THE MOFFAT SERIES. 275 



exposed as far as the foot of Easter Burn, much of the section being 

 buried under clay and boulders. The remainder of the traverse is 

 formed of the various zones of the Birkhill Shales, from the D.-vesi- 

 culosus band to that of M. spinigerus. They are capitally shown in 

 the banks of Easter Burn, and afford an abundance of Graptolites, 

 especially of those of the zone of M. gregarius, the peculiar varie- 

 gated strata of which are very conspicuous in several small quarries 

 on the left of the stream. The deepest beds exhibited are greatly 

 disturbed ; but the strata gradually assume their natural position 

 towards the southern margin of the band, where a few of the highest 

 grey- shale beds are cut out by a small fault at their point of contact 

 with the greywackes. 



This single section might perhaps be regarded as affording suffi- 

 cient proof of the identity of the strata of this band with the Moffat 

 beds already described, and of their corresponding inferiority to the 

 greywackes. The evidence is defective, however, in demonstrating 

 the presence of any thing older than the Birkhill Shales, and in de- 

 fining the relation of the latter to the greywackes to the south. 



Black Grain (Plate XIII. Plan C ; fig. 12). — These missing links 

 in the chain of evidence are both supplied by a remarkable section of 

 the rocks of the band in Black Grain, a small stream descending the 

 opposite slope of the watershed, about two and a half miles to the 

 south-west of "Whitehope. Between the two localities the band can 

 be traced almost continuously by the usual N.E. and S/W. depression 

 due to its presence, as well as by the occasional exposure of the 

 characteristic shales and mudstones along its course. 



Eig. 12. — Black Grain. (Sketch Section.) 



1ST. 



D. Cliff of purple flagstones. 

 Cb. Grey and purple shale, with black and white seams. 



3. Zone of Bastrites maximus. 2. Zone of Monograptus spinigerus, 

 Ca. Hard black flags and shales. 



B. Contorted pale mudstones with black seams. 



In Black Grain the greywackes of the country dip outwards from 

 the margins of the band, both to the north and south. To the north 

 the succession is unintelligible. To the south the greywackes form 

 the summit of a steep cliff, which here causes an abrupt deflexion of 

 the stream-course. They visibly overlie a great thickness of grey 

 and purple shales, containing black seams and thin lines of white 

 and yellow clay. 



These are clearly the Upper Birkhill Shales. They yield in abund- 

 ance the characteristic fossils Rastrites maximus (Carr.) and Mono- 



