MEMORANDA. 805 



in a state of unhoped foi' perfection, but also furnished abun- 

 dance of the minute forms. Having obtained by this method 

 highly satisfactory results from specimens from many localities, 

 I can confidently recommend it as an addition to our modes 

 of research. 



The following directions will enable any one to apply the 

 process. Put small lumps of the mass to be examined into a 

 test tube, with enough of a solution of caustio potassa or soda 

 to cover them ; then boil over a spirit lamp for a few seconds, 

 or a few minutes, as the case may require. If the solution is 

 sufficiently strong, the masses will rapidly crumble to mud, 

 which must be poured at once into a large quantity of water, 

 which after subsidence is removed by decantation^ If the 

 mass resists the action of the alkaline liquor a still stronger 

 solution should be tried, as while some specimens break up 

 instantly in a weak solution of alkali, others require that it 

 should he of the consistence of a dense syrup. The mud also 

 should be poured off as fast as it forms, so as to remain as 

 short a time as possible in the caustic ley. 



The only specimens which I have found not to give good 

 results by the method above given, are those from Tampa Bay, 

 Florida, and the infusorial marls from Barbadoes. In the 

 masses from Tampa the lapidification is so complete, that the 

 alkali destroys the shells before the lumps break up ; and in 

 the case of the Barbadoes marls the cementing material is cal- 

 careous, and requires a dilute acid for its removal. In apply- 

 ing the above process one caution is necessary, which is 

 to thoroughly wash the shells with icater^ and not with acids, 

 as the latter will cause the deposit of a portion of the dis- 

 solved silica and materially injure the beauty of the speci- 

 mens. When the washings are no longer alkaline, the 

 specimens may then be thoroughly cleansed by acids or by 

 the chlorate process described in the last number of this 

 Journal. (Vol. xxi. p. 145.) — J. W. Bailky, American Journal 

 of Science and Arts, 2nd Series, Vol. XXI, May, 1856. 



On the JVon-Existence of Polarizing Silica in the Organic King- 

 doms. — It is now more than twenty years since Sir David 

 Brewster announced the existence of polarizing or doubly-re- 

 fractive silica in the cuticle of Equisetum, and in that of some 

 of the grasses. In Lindley's ' Natural System of Botany,' the 

 following account of Brewster's experiments is given : — " On 

 subjecting a portion of the cuticle of Equisetum hyemale to the 

 analysis of polarized light under a high magnifying power, 

 Brewster detected a beautiful arrangement of the siliceous 

 particles, which are distributed in two lines parallel to the 

 axis of the stem and extending over the whole surface. * * * 



