British Association: 45 
Another addition to the structure of this interesting Paleozoic 
Echinus, made by Mr. Baily, was the discovery of spines which he 
had observed on a specimen of the same species, also from Hook 
Point, in the Collection of the Geological Survey of Ireland, a 
number of the minute spines still remaining attached to the plates, 
the principal tubercles on which are perforated, and surrounded by 
a circle of smaller ones. These spines were less than a tenth of an 
inch in length, and, on examination with a microscope, were found to 
be longitudinally striated. 
ON THE SIGNIFICANCE OF THE SrQueNce oF Rocks anp Fosstrs. By Harry 
Srevey, F.G.S. 
AVING assumed as axioms, that clays are the mud of rivers, 
that sandstones are the detritus of old crystalline rocks, while 
limestones were organically or chemically formed, the author con- 
trasted the Cretaceous and Jurassic Rocks, and the sequence of the 
beds forming them; and, from the alternations of the strata, he 
deduced the alternations of the upheaval of continents and the 
nature of the rocks presented for denudation. He then, by way of 
illustration, worked out the physical geography of the Cretaceous 
period, as evidenced by the rocks of the Eastern and Northern 
Counties ; and, having considered the effect of these physical revo- 
lutions upon the fauna of the ocean-floor, it was concluded that the 
operation of elevation and depression, in the ways pointed out, might 
produce all the phenomena of existing life-provinces on land and by 
sea, and similar life-provinces in the seas of past time. It was then 
shown that breaks between strata do not generally indicate denudation 
or breaks in time, but merely upheaval or depression of old lands, 
bringing into wear newrock-material, and causing the immigration of 
a new province of marine life. Mr. Seeley then showed that life was 
no measure of time; and concluded by controverting the teaching 
of Lyell, Forbes, Haughton, Hennessey, &c., that fossil species are 
any evidence of change of climate. He showed that one existing 
species could not tell anything about the climatal conditions of an- 
other, and therefore that the climate of extinct genera and families 
could not be inferred from existing analogues. The old faunz were 
not universal; nor could the existing analogues have reached their 
present homes without wandering through very different climates. 
Evidence was adduced of extensive migrations, and it was concluded 
that in old times the species migrated, not the climate. 
CORRESPONDENCE. 
—— 
To the Editors of the GroLocicaAL MAGAZINE. 
I Turk that it might be of service to those who, like myself, live 
in the neighbourhood of deposits containing the remains of Elephants 
and other large Mammalia, if you would describe the method that 
was used to extract the tusks of the Lford specimen of Elephas primz- 
genius from the matrix. I have secn many tusks ruined by unskilful 
