400 



THE GEOLOGIST. 



manner: — A current of chloride of silicium is brought through a 

 tube, terminating by a glass funnel, the wide opening of which just 

 touches the surface of water. The chloride of silicium is decomposed 

 in presence of water, even before it comes in contact with the liquid, in 

 the damp air contained in the funnel, and hydrophane is deposited upon 

 the sides of the latter. It is translucid vt^hen wet, opaque when dry, 

 and becomes translucid again whenever it is placed in contact with water. 

 Analyzed, it gave a formation similar to that of resinitt? : — 



(S i 0^)^ 2 H 0 



or, water 11 '68; silicic acid, 88-32. 



NOTES AND QUERIES. 



Potato Disease.—" The early re-appearance, tlils season, of fche potato disease 

 in the Midland Counties, induces me to call the attention of practical geologists 

 to the subject; for perhaps I may not err in supposing that soil exei-cises great 

 influence in the developement of the disease. In the year 1855, when travelling 

 from this place to Penman Mawr, I was forcibly struck by the fact, that whilst 

 all the potato fields in the district occupied by the varieties of the 'New Eed 

 Sandstone, through which my course lay, exhibited unmistakeable signs of this, 

 disease, no sooner were the older strata, whether carhoniferous or Silurian, 

 entered upon, than all the potato crops presented a perfectly healthy 

 appearance. Again, in the autumn of last year, ail the potato crops in this 

 region suffered in a greater or less degree ; whilst, as I was informed by an eye- 

 witness, in the carboniferous and other strata of iNTorthumberland and Cumber- 

 land, the potato crops were wholly free from this disease, although the weather 

 in that part of England was so wet and ungenial at the time, that the crops of 

 corn suffered greatly from excess of moisture. It has occurred to me as by no 

 means improbable, that, by a proper admixture of soil, this serious evil might, in a 

 great measure, be suppressed, if not wholly eradicated; and, if agricultural 

 geologists would, through the medium of the Geologist, furnish reports of the 

 districts in which the disease is particularly prevalent, and of those v/here the 

 crops are healthy, it might lead to very beneficial results, — E. M. Zoe]n^lin, 

 Kenilworth, August, 1858." 



Classification of the Purbeck Beds. — " Sib, — As a student of geology, I have 

 been much puzzled with the classification of the Purbeck beds; some authors 

 representing them as belonging to the Wealden, others to the Oolite, and some 

 again as being a distinct formation. Can you inform me, through your invaluable 

 Journal, which is most correct. Also, of the origin of the popular belief in the 

 existence of coal beneath Blaekheath, near London. — Yours obediently, X. Z. 

 FoLisiL." — The Purbeck and Wealden deposits are probably contemporaneous vdth 

 certain lower Cretaceous marine beds, which are to be found existing in France 

 and Switzerhmd, and were, tlierefore, anterior in age to our greensnnd and chalk, 

 th' iigli (o s(>-;ne Gxtcat our lower greensand intercalates with the Upper Wealden 

 beds. 'I'lio l ivers of the Oolitic, Wealden, and early Cretaceous period evidently 

 run l,,)in ilio snnic huuls, though these v\^ere progressively modified in extent, and 

 "^"^^ ' y si' w, holding, as ages advanced, successively modified faunas. In 

 I ni' ■'■^-•e, therefore, the Purbeck and Wealden indicate a transitional 

 period ^(M^^('!'n i\\c .Invns^ic and the Cretaceous periods, partaking in the animal 

 nnd YOtA'tM ;i!>U' ( li;u-;irirrs of each, 



