cxlii GENERAL SUMMARY OF SCIENTIFIC AND 



The Microscope in Geology. A valuable paper on the mi- 

 croscopic rock-structure of some ancient and modern volcan- 

 ic rocks was lately read before the Geological Society by 

 Mr. J. Clifton Ward. In this paper he gives the details of 

 structure of some modern lavas, showing that even in such 

 modern lava-flows as that of the Solfatara, considerable 

 changes had taken place by alteration, and the replacement 

 of one mineral by another, and this very generally in succes- 

 sive layers corresponding to the crystal outlines. With re- 

 gard to the ancient lavas and ashes of Cumberland of lower 

 Silurian age, they resembled the Solfatara graystone, and 

 though in external structure having more of a felditic than 

 a basaltic appearance, in internal structure they have consid- 

 erable analogies with the basalts, while in chemical composi- 

 tion they are neither true basalts nor true felstones. 



In the case of the Cumbrian ash-rocks the most intense 

 metamorphism had taken place ; and the author states that 

 neither the careful inspection of hand-specimens, nor the 

 microscopic examination of thin slices, would in all cases 

 enable truthful results to be arrived at, but that these meth- 

 ods and that of chemical analysis must be accompanied by 

 a laborious and detailed survey of the rocks in the open 

 country. 



Botany. We notice as worthy of attention the articles now 

 in course of publication in the Monthly Microscopical Jour- 

 nal, by Thomas Taylor, microscopist of the United States De- 

 partment of Agriculture, " upon certain fungi parasitic on 

 plants." In the March number he describes the " black 

 knot " of cherry and plum trees, and the Oidium tuckeri 

 found on the vine. The latter appears to be not a true 

 mould, but merely a condition of Erysiphe, a true parasite 

 of the vine, which will not fruit when removed from the 

 plant on which it grows. 



Hitherto no DiatomaceaB are certainly known to have been 

 found earlier than in tertiary deposits. The few so-called 

 diatoms found by Dr. White in the hornstone of the Devo- 

 nian are exceedingly doubtful. We should scarcely expect 

 silica imbedded in silica to be very visible. Very recently 

 Count F. Cartracane, a well-known microscopist, states, in 

 the JVaturforscher, that he has proved the existence of Dia- 

 tomacea3 during the coal period. A piece of Lancashire 



