556 DR. F. H. HATCH ON THE SPHEROID-BEARING 



concentrically arranged scales of biotite or dark hornblende. This, 

 for instance, is the case in the Pudding-granite of Craftsbury, Yer- 

 mont *, where, in addition to the biotite, they contain small quanti- 

 ties of muscovite, quartz, felspar, and calcite f. 



In an interesting paper read before this Society in 1879 the late 

 Mr. J. A. PhOJips t gave the results of a series of careful investiga- 

 tions into the nature of the dark-coloured, so-called " concretionary 

 patches." His conclusions show that these bodies differ from the 

 enclosing rock, first, by containing a larger proportion of dark mica 

 and hornblende ; secondly, by their greater basicity, the orthoclase 

 of the matrix being replaced by plagioclase in the concretion, or by 

 the latter being poorer in quartz than the matrix. Although several 

 of the concretions described by this author are spheroidal or ovoidal 

 in shape, they present neither radial nor concentric structure. 



Yom E-ath § has mentioned the occurrence of flattened spheroids, 

 of 6-8 centim. diameter, in the hornblende-granitite of Slatmossa, 

 Kirchspiel Jareda, Kalmalen, in Sweden. These bodies have a gra- 

 nular nucleus, composed of the granite-forming minerals, and a 

 narrow peripheral zone, showing radiate structure. The latter is 

 further subdivided into an inner felspathic layer and an outer darker 

 sheU. rich in biotite and hornblende. The same author l| has de- 

 scribed similar bodies in the granite of Eonni, in Sardinia. They 

 were originally discovered by Prof. Lovisato ^, while on a visit to the 

 island. The balls occur, as at MuUaghderg, packed together in a 

 small space, scarcely exceeding two cubic metres in extent. 



The spheroids from Fonni have quite recently been submitted to 

 a careful examination by Fouque ** ; and his description of them 

 shows that they exhibit several striking points of resemblance to the 

 Irish specimens. Like the latter they consist of two parts : — (1) a 

 nucleus, similar in composition to the surrounding rock ; (2) a 

 marginal portion composed of plagioclase felspar (albite) and biotite, 

 the felspar being in divergent rays, and the mica in concentric zones, 

 in which the individual plates are disposed in a tangential manner 

 with respect to the nucleus ft- 



* Report on the Geology of Vermont, by Ed. Hitchcock and others, vol. ii. 

 (1861), pp. 564, 721. 



Also, G. W. Hawes, Concordia, 1878, pp. 190-204. 



t M. K. de Kroustschoff, Bull, de la Soc. Mineral, de Fr., vol. viii (1885), 

 p. 138. 



\ Quart. Journ. Geol. Soc. vol. xxxv. 1879, p. 1. 



§ Sitzungsber. der niederrhein. Ges., Dec. 1874, p. 206. See also a paper 

 by N. O. Hoist and F. Erichstadt— Geol. Foren. Stockh. Forbandl. No. 86. 

 Bd. vii. Haft. 2 (1884), p. 134 — where the Slatmossa rock is incorrectly desig- 

 nated Klotdiorit. 



II Sitzungsber. der niederrhein. Ges., Juni 1885, p. 201. 



% Ibid., Juni 1883, p. 131. 



** " Sur les nodules de la Granulite de Ghistorrai pres Fonni (Sardaigne)," 

 Bull, de la Soc. Mineral, de France, tome x. (1887), pp. 57-63. 



ft Prof. Judd has kindly lent me, for comparison, a specimen of these 

 spheroids. It is considerably flattened : the largest diameter is about 4-| inches, 

 the shortest not more than 2 inches. The zonal portion, which is about 1 inch 

 in width, contains dark mica, but only in the outermost layers, the remainder 

 being composed of pure felspar in divergent rays. 



