TRANSACTIONS OF THE SECTIONS. 59 
ditions and forms under which the forces which cause these motions are exerted, 
and under which such phenomena exhibit themselves, as follows. First, when the 
substances have to be brought into a fluid state by dissolving them in water, 
alcohol, &c., for the purpose of crystallization or for dialysis, as shown by the 
beautiful researches of Professor Graham. Secondly, when the substances are 
brought into a fluid state by heat, as is usually done with metals, such as lead, 
antimony, &c., when it is intended to crystallize them for their purification ; but 
the most remarkable instances are those in which the motion of molecules takes 
. place without there being such facilities afforded to the mobility, as in the previous 
divizion the substance remaining in a solid state. The third division was where 
the change was produced by mechanical means, asis shown by the change of mal- 
leable fibrous iron by means of concussion into a crystalline and brittle form. 
Fourthly, the existing cause may be chemical action, of which hitherto only a few, 
but those very interesting, instances have been noticed. Another instance of 
molecular motion under the excitement of chemical action observed in the manu- 
facture of white lead bythe Dutch process, as used in this country, is the object of the 
paper. Thin sheets of metallic lead are exposed at a temperature rarely exceeding 
180° Fahr. to the action of the atmospheric air, mixed with the vapour of acetic 
acid and carbonic acid. They are converted into carbonate of lead ; but when the 
lead used for this purpose has not the necessary purity, there are observable in the 
parts oxidized atid converted into carbonate of lead layers of different tints, and 
especially the thin layer nearest to the remaining portion of metallic lead shows a 
decided difference in colour, being darker and generally of a reddish-grey hue, 
arising from the oxides of iron, copper, &c.; and the remaining portion of the me- 
tallic lead, on being analysed, also showing an increase of the impurities. 
GEOLOGY. 
Address of the President, Wartneton W. Suytu, W.A., F.R.S., F.GS., Chief 
Inspector of the Minerals of the Crown and of the Duchy of Cornwall, Lec- 
turer at the Royal School of Mines, Jermyn Street. 
IF there is any one part of the British Islands where the very name of the place is 
naturally associated in our minds with a particular geological formation, it is the 
town of Newcastle as associated with the Coal; and beyond a doubt many of the 
present visitors to this cradle and centre of the coal-trade will have made their 
ourney hither with the expectation of not only hearing communications on various 
faphiches of geological science, but more especially of adding something to their 
knowledge of the carboniferous strata. 
We are to be favoured with several papers dealing with different portions of the 
subject, and I am led to think that, with a view to their scope being fully appre- 
ciated, as well as for other reasons which I propose to set before you, it may be 
advisable that I should invite your attention to the state of our knowledge of the 
occurrence and history of the coal-measures generally, whilst I refer mainly to the 
a which characterize that most valuable region in which we are assem- 
led. 
In the short time which I will allow my Address to subtract from the hours 
which we require for the reading and discussion of the numerous papers already 
sent in, I shall only attempt as it were an overture, giving a general outline of the 
carboniferous plot, and introducing a few notes to illustrate those passages which 
are most likely, in our successive acts, to demand attention and concentrate our 
interest. 
The Carboniferous System is commonly divided, for convenience sake, and in 
accordance with the structure of most European coal-fields, into three principal 
divisions, viz. the Carboniferous Limestone, the Millstone Grit, and the Coal Mea- 
sures. 1 need here say nothing of the Devonian or Old Red Sandstone system, or 
of the still older rocks which, in the absence of the Devonian, form the foundation 
of that great division of the geological scale with which we are engaged. The 
