ON THE STOCKDALE SHALES. 731 



cation and mapping. He remarked that the thin Moffat series of 

 South Scotland represented the whole of the Llandeilo, Eala, and 

 Llandovery formations in other regions. There was never any 

 doubt as to the general age of the beds above and below these 

 Stockdale Shales, but there had been a great controversy as to the 

 age of the shales themselves, which the Authors had now settled. 

 The zones they had detected in the Lake-district agree with zones 

 already established in South Scotland, Wales, Scandinavia, &c., and it 

 is clear that the ideas of correlation by means of such zones are 

 destined to be generally accepted. 



He commented on the small thickness of these Stockdale beds, 

 but pointed out that they were represented by very great thick- 

 nesses of deposit elsewhere ; thus the Browgills were represented 

 by thousands of feet in the Gala group and the Tarannon, and the 

 Skelgills by enormous thicknesses in Girvan and Central Wales. 

 The Authors had accomplished a piece of work of the highest sys- 

 tematic importance. Further zone-work was required, and it would 

 be followed by a remapping of many areas. 



Prof. Hughes alluded to the enormous changes in the classifi- 

 cation of the older Palaeozoic rocks which resulted from Prof. Lap- 

 worth's researches in the Moffat area. He referred to the appa- 

 rent absence of reappearances of fossils in the beds described, 

 but pointed out an instance of such a reappearance of a group of 

 fossils elsewhere. He noticed the absence of fossils in the upper 

 Browgill Beds of Spengill, and speculated on the possible con- 

 nexion of this with the red coloration of the rocks. He thought 

 that we must not overlook the important question whether the ap- 

 plication of the Graptolitic and Trilobitic verniers would give the 

 same results. He contrasted our present knowledge with the state 

 of things when he mapped that country. 



Dr. WooDWAED noted the fact that in the case of these thin beds 

 a fauna limited to a small thickness of them was found to extend 

 through a much greater thickness of rock elsewhere. With regard 

 to the relative value of fossils, he pointed out that we must make 

 the most of what we can get. 



Mr. HoPKiNsoN had examined the beds many years ago, and, 

 although he had not worked out the zones, his recollections of the 

 general succession coincided with the views of the Authors. 



Mr. Etheeidge commented on the value of zones, and specially 

 referred to Prof. Keeping's work in Central Wales, and that of 

 Prof. Blake on the Kimmeridge beds of the north of Prance and the 

 Yorkshire Lias. 



Dr. HiNDE referred to the value of the large series of specimens 

 exhibited in showing the characters of the rocks and fossils 

 described. 



Mr. Ptttley pointed out the difficulty of restoring the physical 

 geography of these early times. 



Mr. Maee, in reply, pointed out that one peculiarity connected with 

 Graptolites was the extremely slow accumulation of the deposits which 

 usually contained them, as might be inferred from the remarks of 



