Geological Society of London. o1o 
instance by a tributary of the Idle; the recession of this valley 
towards that of the Trent (assisted by other causes) probably led to 
the diversion of the latter river from its original transverse valley 
into that of the Humber. _ 
The study of these changes in the river-courses of Lincolnshire 
leads to the conclusion that whenever a succession of ridges and 
depressions has been developed out of the surface of a country, 
a river crossing any one of the longitudinal valleys which happens 
to stretch to the sea-coast is liable to diversion by the backward 
extension of a stream draining directly into the sea from the 
termination of the longitudinal valley. 
3. “On the Section at Hordwell Cliffs, from the top of the Lower 
Headon to the base of the Upper Bagshot Sands.’”’ By the late H. 
B. Tawney, Hsq., M.A., F.G.S., and H. Keeping, Hsq., of the Wood- 
wardian Museum. Communicated by the Rev. O. Fisher, M.A., F.G.S. 
The authors, after a brief sketch of the literature of the subject 
and of the method which they have adopted in measuring the beds 
in the Hordwell section, passed on to describe these, viz. the fresh- 
water Lower Headon series and the so-called Upper Bagshot Sands 
of the Geological Survey. They make the whole thickness of the 
former 831 feet. The bed numbered 382 in their section they 
identified with the Howledge Limestone on the other side of the 
Solent. It is almost the highest seen in the section, and underlies 
the true Middle Headon which is now no longer exposed. The 
authors pointed out that in their opinion the late Marchioness of 
Hastings and Dr. Wright have somewhat misapprehended the posi- 
tion of these several beds. Details were then given of the remainder 
of the section, and comparisons made with the details published by 
former authors; after which the authors described the underlying 
estuarine series, or Upper Bagshot Sands, which has a thickness of 
174 feet. 
4, “On some New or imperfectly-known Madreporaria from the 
Coral Rag and Portland Oolite of the Counties of Wilts, Oxford, 
Cambridge, and York.” By R. F. Tomes, Esq., F.G.S. 
The author, after pointing out the poverty of the British Corallian 
rocks in genera and species of corals as compared with the strata of 
equivalent age on the continent, proceeded to describe a section in 
the Middle Oolite at Highworth. 
The author then described species of Astrocenia, Dimorpharea, 
and Latimeandrina, genera not hitherto recognized in the British 
Corallian ; and for one of the forms he has discovered, he proposed a 
new genus to which he gives the name of Crateroseris. The paper 
concluded with some remarks on the well-known Isastrea oblonga 
of the Portland beds. 
5. ‘The Geology of Monte Somma and Vesuvius, being a Study 
in Vulcanology.” By H. J. Johnston-Lavis, Esq., F.G.S. 
The author, after referring to the vast amount of literature which 
has appeared dealing with the same subject, stated that his object 
was to lay before the Society the results of his personal observations. 
The external form and general features of Monte Somma having 
