1850.] CLEGHORN ON THE TILL SHELLS. 385 



Moeris, on the banks of the Nile at Semne in Nubia ; and having 

 referred to the hypothesis proposed by Prof. Lepsius, in explanation 

 of the great difference (26 feet 8 inches, English) apparent between 

 the highest ancient level of the water of the Nile, as indicated by the 

 uppermost of the markings, and the highest level of the water during 

 the inundations of the present day, viz. that the bed of the Nile in 

 Nubia has been excavated to a depth of 27 feet during the last 4000 

 years ; proceeded to inquire into the physical and geological features 

 of the Nile Valley in Nubia, noticing the power of the stream and 

 the hardness of fts bed — including the volume and velocity of the 

 river, its depth and degree of inchnation, and the lithological 

 character of the rocks over which it passes- After a lengthened con- 

 sideration of these important conditions, Mr. Horner arrived at the 

 conclusion that any wearing away of the bed of the channel north of 

 Semne, the site of these ancient nilometric markings, could not have 

 taken place within the historical period. The only hypotheses that 

 in the author's opinion could meet the requirements of the facts ob- 

 served, would be either the wearing away of a reef or barrier at the 

 place in question, — a process requiring too long a period, — or the ex- 

 istence at some distant period of a dam or barrier, formed perhaps by 

 a landslip of the banks, at some narrow gorge in the river's track 

 below Semne, which in the course of time had again been washed 

 away : — ^but of the existence of any such contraction of the channel 

 where such a barrier was possible, the author stated there is as yet 

 no evidence ; and he concluded by observing, that the conditions at- 

 tending" these markings, at present so enigmatical, offer an interesting 

 problem to any geologist, well-versed in the questions of physical 

 structure involved, who may hereafter visit Nubia. 



April 24, 1850. 



Douglas Denon Heath, Esq., was elected a Fellow. 



The following communications were read : — 



1. On the Till near Wick in Caithness. By John Cleghorn, 

 Esq. [Communicated hy the President.^ With a Note on the 

 Shells found in the Till hy Mr. Cleghorn. By James 

 Smith, Esq., F.G.S. 



\Ahstract7\ 



In examining the Boulder Clay or Till that occurs on both sides of 

 the Bay of Wick, as a thick deposit of very hard greyish clay, and 

 in almost every district of the county of Caithness, the author had 

 particularly noticed the fragmentary state of the majority of the con- 

 tained shells. In accounting for this phsenomenon, he considered as 

 inadmissible the action of icebergs grating over the sea-bottom, which 

 has been brought forward by some as sufficient explanation of the 

 existing condition of these shells. The larger and stronger shells 

 would be broken, as is here the case ; but the smaller and more 



