89 
Do the clay dams across the pre-glacial Wear valley and 
other similar valleys mark epochs in the decline of the ice 
when the retiring glacier for a time advanced again and 
mounted up a huge mass before it ? It is possible, of course, 
that they do not really differ from the rest of the denuded 
drift, but on the other hand they appear in some degree to 
correspond in Weardale and Eskdale, the to two cases I know 
best. Lealhohn corresponds to Bishop Auckland : above 
these points in both valleys I have not noticed any great 
filling-up of the valleys. One can even fancy a correspond- 
ence between some of the clay dams in the one valley and 
in the other as regards relative position and completeness. 
Mr. Thomas Cabnelley, B.Sc., exhibited and explained 
the action of Edison’s Electric Pen. 
Ordinary Meeting, March 7th, 1876. 
Edward Schunck, Ph.D., F.R.S., &c., President, in the Chair. 
Mr. R S. Dale, B.A., exhibited Specimens of Crystals of 
Sulphate of Lead found in Alum Residue, and said that ‘‘In 
the manufacture of pure red liquor (alumina acetate), lead 
sulphate occurs as a bye-product from the admixture of 
alum and lead acetate. This lead sulphate is filtered to a 
stiff paste. In a cask of this pulp the very curious crystals 
I exhibit were found embedded in the centre of the mass, 
and, so /ar as could be seen, unattached. These crystals 
resemble the axes of a crystal of the regular system, 
and are undoubtedly pseudomorphs from crystals of alum. 
Lead sulphate in the crystalline state belongs to the Rliom- 
hie system. In the same cask crystals of alum were found, 
which leaves little doubt that such was the origin of these 
extraordinary forms. Analysis showed them to consist of 
lead sulphate.” 
