l893-] NEW-YORK MICROSCOPICAL SOCIETY. 17 



The following Committee on Annual Exhibition was appointed 

 by the Chair : Dr. E. G. Love, Dr. F. D. Skeel, Mr. Charles S. 

 Shultz. 



The Corresponding Secretary read a communication from Mr. 

 K. M. Cunningham, dated Houston, Texas, October 28th, 1892, 

 accompanying the donation of a package of tripoli, as follows: 



"I forward to the Society a cabinet specimen of tripoli de- 

 rived from a superficial outcrop near Navasota, Texas. After 

 having submitted it to a micro-analysis I am able to present the 

 following points of interest in relation thereto. The deposit pre- 

 sents a striking interest geologically, as it appears to be of com- 

 posite origin, as developed during its analysis. Ninety percent of 

 the mass may be regarded as made up of what may be alumina in 

 its most highly divided state, or, if not alumina, an amorphous sil- 

 ica, all of which may be completely removed by elutriation. The 

 heavier sediment remaining is found to be volcanic glass, or some 

 like product of igneous fusion, as indicated by its physical char- 

 acters, viz., complete transparency, flat angular fragments, free- 

 dom from admixture with the ordinary silicious, rounded, and 

 abraded grains derived from the decomposition of the azoic or 

 granitic rocks, and whose protean distribution is known to all who 

 have made sands a study. The particles composing this glass are 

 further characterized as being thin plates, filled with vesicles and 

 tubuli, which are very evident in any of the media used in an ex- 

 amination of the same. Examined dry (in air), the vesicles or 

 minute bubbles are very evident, while in balsam they are nearly 

 obliterated. Likewise the tubuli in balsam are differentiated or 

 made quite plain, and finally become indistinct as the balsam in- 

 vades the air channels of the tubuli; and if the study is made 

 with bisulphide of carbon as a medium, the fragments and plates 

 show with double intensity. (The bisulphide of carbon I refer 

 to is used for patching shoes, and costs ten cents a bottle any- 

 where, and is called 'quick cement,' and offers a useful medium 

 for the immediate study of diatoms, giving intense and brilliant 

 images before evaporation takes place.) 



" If it be admitted that this glass is of volcanic origin, we must 

 necessarily recur to the conditions under which it became a part 

 of this deposit. To do so we are brought face to face with the 

 hypothesis of volcanic dust showers, transported through aerial 



