326 SECTIONAL TRANSACTIONS.— C. 



activity. Associated implements range from Acheulean to Aterian (Early 

 Upper Palaeolithic). 



(Full accounts of the hydrography and physiographic development vi^ill be 

 found in the Geological Magazine, September 1932, and in the Geographical 

 Journal, 1932.) 



Afternoon. 



Excursion to Helmsley, Stamford Bridge, etc. 



Friday, September 2. 



Symposium on The relations of the Millstone Grit to the Carboniferous 

 Limestone (Prof. W. G. Fearnsides; Prof. G. Hickling; Miss E. 

 Dix and Prof. A. E. Trueman ; Dr. W. B. Wright ; Mr. L. H. 

 ToNKS ; Dr. R. G. S. Hudson) :— 



Prof. G. Hickling. — Carboniferous earth-movements in relation to the 

 millstone grit problem. 



The Lower Carboniferous rocks of the Pennine area show marked evi- 

 dence of contemporary folding, indicated both by changes of thickness and 

 facies and by the occurrence of local unconformities. The three main 

 tectonic units of the region — the Northumbrian, North Pennine and 

 Derbyshire domes — were marked out during this period. On these 

 elevations the Lower Carboniferous rocks are relatively thin and unfolded, 

 in contrast with the thick development of deeper-water facies found in the 

 intervening troughs of south Northumberland and the Bolland-Skipton 

 area. The rocks in the troughs are strongly folded, and evidence is adduced 

 to show that this folding was largely contemporaneous. The ' Millstone 

 Grit ' type of lithology becomes dominant at different horizons in different 

 districts, but there is no evidence that any major discontinuity in sedi- 

 mentation is associated with the advent of these conditions. 



Miss E. Dix and Prof, A. E. Trueman. 



The problem of selecting a suitable boundary between Lower and Upper 

 Carboniferous varies in its nature in different areas. In South Wales a 

 natural base is frequently provided by an unconformity which usually 

 separates rocks of Carboniferous Limestone type from rocks of more or less 

 typically Millstone Grit type. This unconformity is of varying extent. 



The faunal evidence indicates that the mid-Carboniferous unconformity 

 is not so great as has appeared to be the case from the interpretations placed 

 on the floral records hitherto available. Recently rich floras have been dis- 

 covered in the Millstone Grit and the lowest Coal Measures in several parts 

 of South Wales which are similar to those of corresponding strata of the 

 north of England, Scotland, and Devon. When these floras are taken into 

 account the supposed discrepancy between the correlation based on the 

 flora and fauna disappears. 



In South Wales the base of the Millstone Grit should be drawn at such a 

 position that it will fall within the unconformity, but its actual position in 

 terms of palaeontological zones is more difficult to fix. There is some 

 evidence that it should fall above the zone of E, which appears to be more 

 closely related to the Lower Carboniferous of this area. This will, of course, 

 involve the transference to the Lower Carboniferous of a small thickness 

 of rocks hitherto regarded as Upper Carboniferous. 



