392 TRANSACTIONS OF SECTION C. 



Huronian period was also marked by considerable igneous activity. The Middle. 

 Huronian has not been found in the regions in which the writer has done much 

 field work, and the Animikie, on the north shore of Lake Superior, seems to 

 be more closely related to the Keweenawan than to the Huronian. In the 

 Keweenawan period the vicinity of Lake Superior was the centre of a region 

 of great igneous activity, and immense sheets of diabase were intruded into 

 the previously formed Animikie and Keweenawan sediments. Much of the 

 Keweenawan igneous rock must be classified, like the Laurentian and Keewatin, 

 largely on a lithological basis, as in many sections there is absolutely no fixed 

 sedimentary horizon in the whole geological scale from Keewatin to Recent. 

 The Keweenawan diabase sills usually have a columnar structure, and in a few 

 places show evidences of differentiation of the magma. 



The writer has never found a distinct fossil in the pre-Cambrian, but he 

 would infer that life existed even back in the Keewatin, because of the 

 presence of limestone, carbonaceous shales, and iron ore, some of which seems 

 to be of bog origin, and also because the more evidence which is collected the 

 more it points to the existence of conditions not unlike those over much of the 

 earth at the present time. 



4. On the Occurrence of a Freshwater Limestone in the Lower Eocenes on 

 the Northern Flank of the Thames Basin. By A. Irving, D.Sc., B.A. 



The limestone was first met with in a well-section at Thorley, on the Herts 

 border. In three other well-sections in the Bishop's Stortford district the same 

 limestone occurs, and in all three of these the limestone is duplicated. These 

 freshwater limestones (often containing traces of freshwater plants) are inter- 

 bedded with the dirty quartzose sands characteristic of the Woolwich and 

 Reading series over a large area, where they are overlain by the pre-glacial 

 stratified gravels, or are proved in other places to underlie the true basement- 

 bed of the London Clay with black flint pebbles, oysters, and sharks' teeth. 

 These facts seem to justify Prestwich's classification of the Oldhaven Beds as 

 belonging stratigraphically to the Woolwich and Reading Beds rather than to 

 the London Clay above; and to show that Whitaker's contention 1 that 'the series 

 is clearly separable from the Woolwich Beds below cannot be sustained.' The 

 fossils contained in the limestone were recognised by Professor McKenny 

 Hughes as a series belonging to the Oldhaven Beds, and afterwards named by 

 Messrs. F. R. C. Reed and W. Keeping at the Sedgwick Museum. 



Fossils from the Thorley Well. 



Chenopus (Aparrhais) Sowerbyi. | Cyrena strigosa or cordata{1) (young). 

 Cardium Laytoni. Psammobia ( ?) sp. 



Gyprina Morrisi. Cytherea (?) sp. 



Cyrena cuneiformis ( ? ) 



We seem to be here on a rough north to south zone of the Tamisian area marked 

 by a coalescence of the conditions under which the typical Thanet Sands (further 

 east) and the typical Reading Beds (further west) were laid down. The 

 absence of the London Clay between the Boulder Clay and these Reading Beds 

 over a considerable distance is somewhat remarkable, as pointing to prequater- 

 nary denudation. 



5. A remarkable Sarsen or Greywether. 2 By A. Irving, D.Sc, B.A. 



Without desiring to add to the existing plethora of literature on these rocks 

 the author thinks that this sarsen is worth special notice. It was discovered 

 last winter in digging a grave in the Bishop's Stortford Town Cemetery about 

 seven feet from the surface in the principal boulder clay of the district, the 

 equivalent of the chalky boulder clay of the Eastern Counties. It has been 

 placed in the grounds of Hockerill Vicarage. 



1 Mem. Geol. Surv., iv., p. 239. 



2 A popular account of this block was given by the author in the Herts and 

 Essex Observer, January 7, 1911. 



