ANNIVERSARY ADDRESS OF THE PRESIDENT. XXVH 
cumulations ; and we may now add, that the Geological Survey has 
not lost sight of the physical history of these deposits during its ex- 
amination of them, while at the same time every attention is given to 
their zoological modifications and changes. We may here call atten- 
tion to a more careful study of the oolitic grains than is sometimes 
given. Whole masses of them are no doubt concentric concretions 
round a minute nucleus, sometimes even appearing to surround a 
small crystal of carbonate of lime ; but others, though of the same 
general shape externally, are merely rolled pieces of corals and of 
shells, much resembling the coarser coral sands familiar to those who 
have examined coral reefs, or shores adjacent to coral accumulations. 
Often both kinds are mingled together m a common drift, diago- 
nally laminated, with larger portions of corals and broken shells, the 
flat parts of the corals and shells commonly parallel to the false 
bedding, thus pomting to the pushing action of moving water along 
a sea-bottom, the careful study of which readily shows the direction 
whence and to which the water moved. Indeed the mechanical ag- 
gregation of a large proportion of the calcareous beds is very striking, 
while the chemical production of others is equally apparent. By the 
careful consideration of these differences in the limestones, of the 
sandstones and of the clays, not forgetting the friction marks from 
moving water, and the trails and other traces of the various molluscs 
and other animals which have moved on surfaces, for the time, 
exposed, the geologist will find his labours well rewarded by an 
insight into the manner in which mineral matter has been deposited 
over a few thousand square miles at this geological period. 
Mr. Nicol, in his communication to the Society on the Silurian 
rocks in the south of Scotland, where they occupy an area estimated 
at 4000 square miles, examined into the manner in which the various 
beds composing it may have been accumulated. Though igneous 
rocks, such as felspar porphyries and the ordinary hornblendie 
varieties, commonly termed trappean rocks, are present in the con- 
glomerates, sandstones and slates, noticed under the head of grey- 
wacke or Silurian Rocks, they would, by the descriptions of Mr. 
Nicol, rather appear to have been intruded among the beds formed 
in water, after the deposit of such beds, than thrown among them 
while accumulating. It is shown, that in tracing the general mass 
from its northern border in Peeblesshire and the Lothians, south 
through Selkirkshire and Roxburghshire to the confines of England, 
and across the strike of the beds, that the coarser varieties of rock 
prevail on the north in large irregular masses, while on the south the 
finer varieties predominate in thinner, more regular, and more di- 
stinctly stratified beds, whence Mr. Nicol concludes that the deposits 
generally have been derived from the north. Hxamining the beds 
themselves he finds a mixture of clay-slates, and sandstones and con- 
glomerates, the former rarely exhibiting any of the cleavage so com- 
mon in parts of Wales and the older Cumbrian districts. The grains 
of quartz in the sandstones are rarely larger than a pea, while the flat 
fragments of a clay-slate attain several inches in length. He discovered 
no traces of granitic rocks, gneiss, or mica-slate rocks in these beds. 
