Page:Quarterly Journal of the Geological Society of London, vol. 27.djvu/368

 tions. He also asked whether the line representing the change in the direction of the pole formed a reentering curve, and whether the theory would account for the climate of Greenland in Miocene times. He suggested changes in the form of the earth which must have affected the direction of its axis.

The President remarked upon the difficulty that arose from astronomical theories differing so much among themselves. He referred particularly to Adhemar's theory, and remarked that the difficulty connected with it is, that it invokes a recurrent cause, which must produce similar effects every 21,000 years, whilst there is very little evidence of glacial action during the whole long period of the Tertiary epoch.

The Author, in reply, stated that he could not go back beyond 30,000 years, but that he thought glacial conditions must recur. He had not astronomical data beyond 2500 years ; and these were very vague. The motion would be the same in kind, but uncertain in degree. His theory was based entirely upon observed facts. In laying down the curve, he considered it safe to go as far as the semicircle, as he had observations covering 40° ; but he could not say whether the curve would be a reentering one, although it showed a tendency that way, and would certainly be very nearly so. With regard to the change of climate of Greenland, as evidenced by its Miocene flora, he was not sufficiently versed in botany to pronounce an opinion. He remarked, in conclusion, that the distance of the earth from the sun did not seem to affect the climate of the Southern Hemisphere, and stated that Venus is at present suffering under a most severe glacial epoch.

3. On Allophane and an Allied Mineral found at Northampton. By W. Douglas Herman, Esq., Student of the Royal College of Chemistry.

(Communicated by W. W. Smyth, Esq., F.R.S., V.P.G.S.)

The only English localities at which, to my knowledge, allophane has been shown to occur are the chalk-pits at Charlton, near Woolwich, the Purley downs, near Croydon, and a spot not far from Tavistock, in Devonshire. Dr. Charles Berrill, however, shortly before his death, discovered a mineral much resembling the Charlton allophane in physical properties in a pit opened in the ironstones of the Northampton Sand (beds of Inferior-Oolite age) in the grounds of the Northampton General Lunatic Asylum. It occurs as an amorphous, translucent, somewhat hard and exceedingly brittle mineral, of a yellowish colour inclining to red, and incrusting the surface of a sandstone rock.

The following analyses of a specimen of this mineral presented by Mr. Sharp, of Dallington, to the Museum of Practical Geology fully bear out, I think, its claim to be called allophane. I append, for the sake of comparison, Mr. A. B. Northcote's analysis of a characteristic sample from Charlton.