268 
Communications made to the Society : 
(1) On a method proposed by M. Fizeau for comparing 
a metre & bouts with a metre a traits. By Profes- 
sor Minin. 
(2) On the section exposed at Roslyn Hill Pit, Ely. By 
T. G. Bonney, B.D. 
The author stated that hitherto two hypotheses had been 
proposed to account for the extraordinary collocation of Boulder 
clay, Cretaceous beds and Kimeridge clay in this pit; (1) 
which had been advocated by Mr H. G. Seeley and others, that 
this was the result of faulting ; (2) that, as had been suggested 
by Mr O. Fisher, the cretaceous beds were a boulder-like mass, 
that had been dropped in boulder clay times from an iceberg 
into a depression which it had excavated in the Kimeridge 
clay. He stated that during the last three years he had fre- 
quently visited the pit with a view of testing these theories. 
He pointed out that if the collocation were the result of a fault 
we should have in the space of about a hundred yards two cor- 
responding down-throw faults bringing down the boulder clay, 
and an inner pair of (relatively) up-throw faults for the creta- 
ceous beds, which latter were reversed faults. He also shewed 
that the lower greensand at the E. end of the pit was not, as 
had been supposed, zz situ, and that the boulder clay at the S.E. 
corner formed a wedge-like mass that ultimately disappeared, 
allowing the gault to come in contact with the Kimeridge 
clay. He exhibited plans and sections, and argued that the 
collocation was in the highest degree improbable on a theory of 
faulting. There was a third hypothesis possible, that the creta- 
ceous beds had slipped from above the Kimeridge clay into 
their present position, but though some appearances favoured 
that, he thought it, on the whole, less probable than the 
