TRANSLATIONS AND NOTICES 



GEOLOGICAL MEMOIRS. 



On the Structure o/" Agate. By Theodore Gumbel. 



[Leonhard u. Bronn's N. Jahrb, f. Min. u. s. w. 1853, pp. 152-157.] 



The curious and beautiful appearances afforded by agates have long 

 made them of primary importance in mineralogical cabinets ; but 

 until of late years particular attention does not seem to have been 

 paid to the internal structure of these bodies. Dr. J. Zimmerman 

 is the first, of my knowledge, who observed* that the different varie- 

 ties of quartz — as amethyst, calcedony, carneUan, jasper — formed the 

 concentric layers of the nodules, which were either hollow or occu- 

 pied with crystals f. 



In the Jahrbuch of the Imperial Geological Institute of Vienna for 

 1851 J is a very interesting memoir on the interior structure of agates 

 by Prof. Dr. Franz Leydolt, where he states that, on being submitted 

 to the action of fluoric acid, the amorphous portions are dissolved 

 before the crystalline layers or bands ; and the agate-surface being 

 thus prepared, it is made use of in printing an exact copy of itself. 

 The six beautiful plates accompanying the memoir perfectly exem- 

 plify Prof. Leydolt' s views, and show, — first, that the parts towards 

 the outer surface consist of several spherules variously combined, 

 which are composed of layers of diverse character ; secondly, that 

 towards the centre of the nodule is a large mass of amethystine 

 quartz, the nucleus of the latter again being formed of very small 

 concentric spherules. 



In the 'Jahrbuch fur praktische Pharmazie,' &c. 1852, is a short 

 paper of mine on the rotatory motion of matter in the amorphous 

 condition, in which I have shown that in a sphere of blown glass the 

 material is not homogeneous, but consists of lamellse overlying one 

 another at varying angles and confusedly distorted. As in the thin 

 pelhcle of blown glass the intimate structure of the soap-bubble is, as 

 it were, fixed, so I sought to make further researches by means of ex- 

 periment on molecular movement, such as can be observed in so many 

 instances. One of the most successful experiments was the use of 

 melted stearine, with which very fine graphite had been mixed, 

 spangles of which easily indicated the intimate motion of the mass. 



* In his Taschenbuch fiir Mineralogie. 



[t See also Mr. Hamilton's Paper on the Agate Quarries of Oberstein, Quart. 

 Journ. Geol, Soc. vol. iv. p. 215. — Tkansl.] 



t Vol. ii. no. 2. p. 124. 

 VOL. IX. — PART II. E 



