Intelligence and Miscellaneous Articles. 437 



convenient and natural line of division between the Upper and 

 Middle Bagshot. 



The Upper Bagshot Sands were then described, and attention was 

 drawn to the abundance of fossils in some of the higher beds. 



The author then referred to the correlation of the Bagshot beds 

 with the Hampshire series, and stated his conclusion that the Middle 

 Bagshot beds are of Middle Bracklesham age, whilst the Upper 

 Bagshot Sands are nearly equivalent to the Lower Barton of Hamp- 

 shire, and are in no way equivalent to the so-called Upper Bagshot 

 Sands of Long Mead End. 



3. "Additional Note on Boulders of Hornblende Picrite near the 

 western coast of Anglesey." By Prof. T. G. Bonney, M.A., E.R.S., 

 Sec. G.S. 



In the 37th volume of the ' Quarterly Journal ' the author de- 

 scribed a large boulder of Hornblende picrite which he had dis- 

 covered near Pen-y-carnisiog. During an excursion last summer to 

 Porth-nobla he had found in that neighbourhood at least eight 

 more. The rock then clearly was not very rare in this part of 

 Anglesey. These exhibited some varietal differences. The author 

 gave some details of their microscopic structure, and an analysis of 

 one identical with the Pen-y-carnisiog rock, kindly made for him by 

 Mr. J. A. Phillips, E.R.S., from which it appeared that this British 

 picrite corresponds fairly well with the picrite of Schriesheiminthe 

 Odenwald, to which in other respects it bears so close a resemblance. 

 Mr. J. J. H. Teall recently called the author's attention to a rock 

 which he had collected on Little Knott, east of Bassenthwaite, which 

 appeared to him to resemble the description of the Anglesey picrite. 

 The author had examined a series of specimens from that locality, 

 and found that macroscopically and microscopically there was a 

 marked resemblance, while the percentages of silica and magnesia 

 were not very different. He thought, then, it was very probable 

 that the Anglesey boulders came from the Little-Emott district. 



LXYIII. Intelligence and Miscellaneous Articles. 

 MICA FILMS FOE POLARIZING-PURPOSES. 

 To the Editors of the Philosophical Magazine and Journal. 



GrENTLEMEtf, 



TT may be worth while to mention, in connexion with Mr. 

 -i- Wright's paper on Crystalline Films published in the Philoso- 

 phical Magazine for this month, that very good, clear, uniform 

 mica films may be found among the thin sheets of mica used by 

 photographers for protecting prints, and sold under the name of 

 " crystal medium." 



The very best and clearest mica (chiefly, I believe, from Italy 

 and America) is sought for by those who prepare these sheets ; and 

 the accuracy and uniformity of the splitting is very great. 



Out of a dozen films, 10 x 6 centim. (carte-de-visite size), I have 

 found at least four which are approximately 5- wave films, uniform 

 in thickness throughout ; and most of the others were so even and 

 clear that they were worth the trouble of splitting into thinner ones. 



Phil Mag. S. 5. Vol. 15. No. 96. June 1883. 2 I 



