Reviews — On the Crystals of Olivine. 465 



Corniferous groups in Western New York. The writer has also 

 found a thin bed, nearly entirelj'' composed of these spores, in 

 Shales of the Hamilton Group, at Arkona, Ontario. The only plant- 

 remains associated with the spores are fragments of Calamites, Lepi- 

 dodendron and Ptilophyton Vanuxemi, but the presence of Lingula, 

 Leiorhynchus, Ganoid scales, etc., shows that the deposits are marine. 

 Hitherto no satisfactory evidence of the affinities of Sporangites had 

 been discovered, but Sir W. Dawson believes that a definite clue has 

 been found in certain fossils lately discovered in shales of Devonian 

 age exposed on the banks of the Carua river and other tributaries of 

 the Amazon. These beds contain Spiropliyton and minute rounded 

 Sporangites, which are " inclosed in considerable numbers, in spherical 

 and oval sacs, the walls of which are composed of a tissue of 

 hexagonal cells, and which resemble in every respect the involucres 

 or spore-cases of the little group of modern acrogens, living in 

 shallow water, known as Ehizocarps." The resemblance is so 

 close to the sporocarps of Salvinia that the author suggests the name 

 of Protosahinia for the plant producing them, when it shall be 

 discovered. In the meantime these sporocarps are ranged under 

 Sporangites, as /S. Braziliensis and S. bilobatus. The similarity of 

 the raacrospores inclosed in the sporocarps to Sporangites Huronensis 

 is so striking in every respect that the author believes that these 

 latter were originally inclosed in similar sacs, which have since 

 perished. 



Sir J. W. Dawson also suspects that the Old Red Sandstone fossils, 

 known under the name of Parka and supposed to be the ova of 

 Crustaceans, may prove to be the fructification of Rhizocarps. It is 

 also suggested that such plants as Psilophyton glabrum and Cordaites 

 angustifolia, of which the fructification is unknown, may have been 

 allied to Rhizocarps. G. J. H. 



VII. — Qn the Crystals of Olivine in the Sands of the Isle 



of bouebon. 



Note sur les Cristaux d'Olivine des Sables be Projection 

 DE la Plaine des Sables (Ile Bourbon.) Par M. Alf. Lacroix. 

 Bull. d. 1. Soc. Min. de France, Mai, 1884, tome vii. p. 172. 



ri^HE note contains a description of the crystals of olivine which 

 JL form a large portion of a bed of sand, more than one metre in 

 thickness, occurring on the Plaine des Sables of the He de Bourbon. 

 The crystals are from 2 to 4 mm. in length, and of unusually perfect 

 forms. They are associated with augite crystals, from 1 to 5 mm. 

 in length. The crystallographic forms observed in the olivine were : 

 m (110), h^ (010), gi (100), g^ (210), a^ (Oil), e* (201), e^ (101). 

 Its composition as determined by M.Velain was SiOo 39-9(3, AI2O3 2-33, 

 FeO 6-28, CaO 2-05, MgO 49-i8— total, 99-80. The observation is 

 one of considerable interest as bearing on the origin of certain 

 serpentines. It shows at any rate the possibility of the occurrence 

 of bedded olivine I'ocks. 



DECADE III. "VOL. I. — HO. X. 30 



