Anniversary Address of the President, H. C. Sorby, F.R.S. 135 
Clays, &e.—The chief portion of the fine-grained clays cannot 
be distinguished from the products of the decomposition of felspars 
and other minerals which can be changed in a similar manner; 
but mixed with this is a very variable amount of fine sand, in 
all probability transported in the compound granules already de- 
scribed. Since the sorting of the material depends upon its 
amount, and on the conditions of the current, there seems reason 
to hope that a further study of the ultimate character of clays 
may throw much light on these questions. Some of these indicate 
that they were rapidly deposited from very muddy, shallow water, 
and others that they were deposited from much clearer and deeper 
water. 
Volcanie Ash Beds in British Strata.—Extensive masses of 
rock have been often described as ash beds, but, when we come to 
examine the detailed structure, their true nature becomes very 
doubtful. Some of them may really have been true ashes, but 
they have undergone so much subsequent change that they are 
now totally unlike the ashes of modern volcanoes. The whole 
question requires much more examination, and the study of the 
subsequent alterations becomes the principal consideration, and 
it would lead me into far too wide a field of inquiry to enter 
upon it now. ‘That true but much altered ashes do exist is, 
however, clearly shown by some beds found at Bathgate, near 
Linlithgow. These show a structure which seems to indicate 
that they were originally a pumice ash, but the vesicles have 
been filled with infiltered mineral matter, and the whole greatly 
altered by chemical changes taking place after deposition. 
Conclusion. 
Leaving then out of consideration such cases, and confining our 
attention to by far the greater bulk of our British non-calcareous 
stratified rocks, we see that a most careful microscopical investiga- 
tion shows that the material was originally derived mainly from the 
chemical decomposition and mechanical breaking up of various 
granitic and schistose rocks, the products having been afterwards 
separated and sorted by the action of currents, and more or less con- 
solidated and changed by subsequent mechanical and chemical action. 
When we come to study the detail, it is also possible to form a satis- 
factory conclusion respecting the share which each of the above- 
named classes of rocks contributed to the formation of each particular 
stratum, and also to answer several questions of great interest in 
connection with the geological history of a very important group of 
stratified rocks, which hitherto have not been supposed capable 
of yielding any such information. Though these conclusions are 
