514 Revieus — The Survey Memoir on ihe Scottish TJfjlands. 



improved sketch-plan, and they describe and illustrate seriatim all ilie 

 more important exposures throughout the whole of the Moffat district. 



It is evident that the authors take it for granted that the reader 

 is already more or less familiar with ni}' paper on the Moffat Series, 

 and many of the new lines of section may be regarded as supple- 

 mentary to, or corrective of, those given in that paper. But the 

 new sections are delightfully clear, the descriptions terse and 

 condensed, and our knowledge of the geology of the district is 

 advanced by some important discoA^eries. 



One of the new discoveries made here by the Survey officers 

 is of especial importance. They have ascertained that typical 

 Glenkiln graptolites range up into the two to three feet of black and 

 grey shales overlying the band of Glenkiln Eadiolarian cherts above 

 the Coenograptus zone. They have therefore properly classed these 

 shales with the Upper Glenkiln, instead of the Lower Hartfell 

 (C Wihoni zone), to which they were assigned by myself. They 

 have recognized this special subzone with its characteristic fossils 

 at Dobb's Linn, Hartfell, etc. This discovery enables us lo 

 correlate with certainty a group of strata characterized by similar 

 fossils which piroved most tantalizing to mj'self and others in the 

 geology of the Leadhills district and elsewhere. 



The sequence of the Moffat graptolite zones having thus been 

 established in the typical area upon an impregnable basis, the officers 

 of the Survey next show how the same palasontological succession 

 obtains in all the exposures of black shales occurring in the Central 

 Belt of the Uplands from St. Abbs Head to the Mull of Galloway. 

 'J'hey unravel by means of these graptolite zones the entangled 

 and complicated rock-formations which occur in the many exposures 

 of black shale in this region, and place before the reader in 

 most instances the proofs of their conclusions in the form of 

 sketch-plans, sections, and lists of fossils. They demonstrate, by 

 means of the evidences they bring forward, the identity of the 

 so-called Axial series with the Queensberry group. They show that 

 in some few places where the anticlinal forms have been mostly 

 deeply eroded, as at Trowdale Glen, etc., the entire Glenkiln Series 

 has been cut through, exposing a well-marked Eadiolarian chert 

 zime below it, and that in two instances at least even this chert zone 

 has been cut through, laying bare a basement series of volcanic rocks 

 which they parallel with the Ai'enig volcanic series of Ballantrae. 



While the Moffat Series remains practically unmodified when 

 followed from Dobb's Linn along the strike of the beds, every zone 

 retaining more or less its typical characters and thickness, it 

 changes rapidly when followed in the direction of the dip — the 

 sheet of overlying greywackes descending deeper and deeper into 

 the series as we pass to the north, replacing each black shale bed 

 in turn, until by the time we have reached the northern limit of the 

 Central Belt, the arenaceous fades has descended to the middle zone 

 of the collective series — the whole of the Birkhill shales and U})per 

 Hiirtfell being there represented by a grand thickness of grey wackes, 

 grits, conglomerates, and shales. 



