C. LAFWORTH ON THE MOFFAT SERIES 245 



alike, dip uniformly to the N.N.W. at high angles. Faults, folds, 

 and inversions are occasionally visible among the greywackes ; but 

 in the dark shales they are astonishingly abundant. In every known 

 locality where the Graptolitic beds are exposed, the majority are in 

 this contorted and dislocated condition, and the attempt to ascertain 

 their interrelationship by lithological and stratigraphical evidence 

 has soon to be abandoned as hopeless. Their separation by zoologi- 

 cal characters appears quite as desperate ; for in many localities 

 every trace of their former prolific fauna has been obliterated ; in 

 others only one or two fragmentary forms are obtainable, and these 

 are limited to a few inches Of thickness of the less altered zones. 

 Even in those bands where the fossils are numerous and well pre- 

 served, the neighbouring exposures have frequently not a single 

 fossil in common. 



It is to the consideration of the numerous facts recently made out 

 regarding the black Graptolitic shales that the present paper will be 

 devoted. These peculiar rocks are quite as abundant in other districts, 

 but it is here that they attain their maximum thickness and yield their 

 most varied fauna. At the same time they are here less metamor- 

 phosed than elsewhere; and consequently here, if anywhere, will the 

 problems they suggest admit of a satisfactory solution. 



In the following pages I shall endeavour to prove that, in spite of 

 the uninviting and, indeed, highly perplexing features of these de- 

 posits as here exhibited, we have actually within the limits of the 

 present district more than sufficient stratigraphical and palseonto- 

 logical evidence to enable us to piece together the shattered frag- 

 ments of this important rock-group, and in this way to fix the 

 original sequence of its component beds, to mark out the distinguish- 

 ing fossils of its various zones, to determine with certainty their 

 geological age, and to point out their representatives in foreign 

 countries. 



§ III. History of previous Opinion. 



It is to Prof. Sedgwick that we owe the earliest detailed notice of 

 the rocks of the MofTat district. In his memoir " On the Geologi- 

 cal Structure and Eelations of the Frontier Chain of South Scot- 

 land " *, read at the meeting of the British Association at Glasgow 

 in 1850, he arranged the rocks of the Southern Uplands into five 

 successive formations. The lowest and most ancient of these for- 

 mations, which he denominated the Moffat Group, embraced the 

 majority of the strata of the present district. It was defined as " a 

 great thickness of arenaceous rocks, in which pyritous and Grapto- 

 litiferous schist abounds to such an extent that the arenaceous beds 

 become sometimes subordinate to it." His second group, for which 

 he proposed no distinctive title, included the much broader mass of 

 greywackes to the northward, apparently destitute of the alumini- 

 ferous schists. 



But the most valuable and important paper hitherto published 

 upon the rocks of the Moffat neighbourhood is the memoir by Prof. 

 * Kep. Brit. Absoc. 1850, pp. 103-4. 



