II 



3. The Moffat Series (16). 



By 1877 he had exhausted his study of the facts in the Moffat 

 district, completed his map, and prepared his memoir for submission 

 to the Geological Society. It was published in the Quarterly 

 Journal for 1878, and at once attracted the interest and sympathy 

 of the younger men, but the incredulity and even hostility of 

 holders of the older views. 



In this memoir he confirmed the conclusions summarised above 

 and, among others, established the following : 



(1) The thickness of rocks here is not abnormally great ; 

 the appearance of thickness resulting from repetition due 

 to inverted folding and faulting. 



(2) Although the graptolite fauna of any one shale band as a 

 whole is like that of any other, within each band there 

 are a number of successive graptolite faunas, associated 

 with variations in lithology, each distinct from the 

 others. 



(3) Within a single shale band two or more of these graptolite 

 faunas are repeated, sometimes more than once. If in 

 the repetition the faunas occurred in inverted order, 

 evidence of overfolding could often be detected ; if the 

 repetition was not in inverted order, evidence of faulting 

 could usually be found. 



(4) The graptolite faunas of a single shale band fall into 

 three chief groups : 



(a) A ' central ' (or lower) one, characterised by 

 didymograptids and nemagraptids, of types 

 known elsewhere in the Llandeilo series (Glenkiln 

 Shales). 



(b) An ' intermediate ' (or middle) one, with dicello- 

 graptids and dicranograptids ; comparable with 

 that of the Bala rocks elsewhere (Hartfell Shales) . 



(c) An ' outer ' (or higher) fauna, with mono- 

 graptids, comparable with those of the Coniston 

 mudstones (Stockdale Shales) and other rocks of 

 Silurian or Llandovery age (Birkhill Shales). 



(5) He was able to divide the higher part of the shales into 

 ten graptolite-bearing zones, four in the Hartfell and six 

 in the Birkhill division. 



(6) The rocks are not abnormally thick ; indeed the whole of 

 the history of the Upper Llandeilo, Bala, and Llandovery 

 rocks is compressed into 200 or 300 feet of black shale, 

 which must therefore have been deposited with com- 

 parative slowness, and, as the lithological characters of 

 the shale show, in deep water, reached only by very fine 

 sediment in small quantities. 



