secretary's report, 1908. 
209 
end of Troller's Gill, which was ascended and an examination 
made of its fine section of the white limestone. On the return 
journey e\ddences of glacial overflow valleys were pointed out 
by Professor Kendall. 
On the following Monday the members drove to Qras- 
sington and visited the well-knowTi knolls of Cracoe, Rylstone, 
and Thorpe. Special attention was paid to the structure of these 
knolls in order to test the theory that they were originally sepa- 
rate islets. Much of the evidence seen did not favour this 
explanation. Large bags of fossils, in beautiful preservation, 
were obtained. 
After dinner, tlie General Meeting was resumed under the 
presidency of Dr. Wheelton Hind, when Mr. J. R. R. Wilson, 
H.M. Inspector of Mines (Leeds), and Mr. Geo. I. Wells (Sheffield) 
were elected members. 
An address was given by Dr. Arthur Vaughan upon the 
principles on which the " zoning " of the fauna of rocks should 
be carried out. He said that zoning must always deal with 
organisms which lived at about the same bathymetrical level. 
The worker, for instance, must not pass from a fairly deep water 
organism to a shallow one and back again. Tliat would be bad 
zoning. Zones once correctly made should give a time-scale 
with which to measure changes of all sorts, and with which ta 
measure also the rate of evolution. In considering evolution, 
one had to consider not a particular species, but a group of 
species which he called a gens. A gens might be described 
as a conformable series, all possessing certain common specific 
characteristics, the essential thing being that there should be 
continuity. Thus a gens might include several genera. Proceeding 
to consider the laws of the introduction of a gens, Dr. Vaughan 
pointed out that the appearance of such a group as he indicated 
was first heralded by a few early forerunners, which, as fossils, 
were very few and scarce. Then they came on in enormous 
crowds. That might be called the main entrance of the gens. 
Then there w^ould be continuous alteration of the structural 
details, but the general plan of the animal would always remain 
the same, the variation being considerable in the complication 
