C. LA.PWOJRTH ON THE MOFFAT SERIES. 



269 



The distinctive fossils of the Lower Birkhill Shales may all be 

 collected at this locality. The upper subdivision is too much broken 

 and altered to yield more than a few rare specimens. 



It is needless to follow this band in its prolongation to the south- 

 west. The exposures already examined amply demonstrate that in 

 this district there are no beds in the rocks of the band that are not 

 visible in our typical section of Dobb's Linn. Wherever the suc- 

 cession from the shales into the greywackes is unbroken, the latter 

 are immediately underlain by the representatives of our highest 

 Birkhill bands, below which occur in their natural order the subja- 

 cent strata of our typical locality. 



Thirlstane Burn. (Plate XIII. Plan B.) 



Midway between the first and second of the black-shale bands, an 

 excellent local exhibition of a portion of the Moffat series occurs at 

 the head of a small stream falling into Thirlstane Burn (fig. 8). 



Pig. 8. — Section at Thirlstane Score. 



D. Purple flagstonesandflaggy shales. 

 Cb. Grey shales with seams of black, 

 i \ Is r R yellow, and white mudstones. 



3. Horizon of Eastrites maximus, 



Monograptus Haiti, &c. 

 2. Horizon of Monograptus spini- 

 gerus ( = 8edgwicki). 

 Ca. Black flags with partings of varie- 

 gated mudstones, &c. 

 (3) Zone of Monograptus grega- 

 rhcs. (2) Zone oiDiplograptits 

 vesiculosus. ( 1 ) Zone of D. acu+ 

 minatus. 

 Bb. Pale and non-fossiliferous mud- 

 stones. 

 /. Fault. 



The shales are first visible about midway along the course of the 

 last-named stream, but the section at that spot is valueless for pur- 

 poses of comparison. At the head of the tributary burn the whole 

 sequence of what are instantaneously recognized as the Birkhill 

 Shales is visible, from the green mudstone of the D.-anceps band 

 into the greywackes. 



A fault traverses the beds obliquely from south to north, and 

 this is crossed at a very acute angle by a subordinate anticlinal line, 

 a little below the greywackes. To the west of this anticlinal the 

 beds are in their natural position; to the east they are slightly in- 

 verted. 



The D. -vesiculosus band forms, as usual, a steep cliff and yields its 

 peculiar fossils in abundance. The M.-gregarius zone with its varie- 

 gated and nodular seams is seen in the sides and base of the cliff, 

 the coloured lines being especially conspicuous in some small bosses 

 on the floor of the score. The grey and black beds of the Upper 

 Birkhill group form both sides of the little anticlinal already re- 



