282 Revieivs — Lartet's and Christy s Reliquice. 



system, yet possesses tlie low specific gravity of 2*2 — 2-3 ; thus by 

 its crystalline character being related to the species Quartz, and by 

 its low density to the species Opal. The crystals, though belonging 

 to the rhombohedral system, the author states, stand in no relation to 

 any of the hitherto observed forms of Quartz. They are in hexa- 

 gonal tables, never simple, but always in twins, mostly of three indi- 

 viduals (Drillingen), from which character the author proposes the 

 name Tridymite, and under this name the mineral will be fully 

 described by him in the next part of his '' Mineralogische Mit- 

 theilungen." The crystals are not pseudomorphous, as has been sug- 

 gested, as by polarised light they behave as doubly refracting 

 optically uniaxial bodies. The Tridymite is found in small but 

 sharply defined crystals in cavities in a volcanic porphyry, accom- 

 panied with iron-glance and acicular crystals of hornblende from the 

 Cerro S. Cristobal, near Pachuca, Mexico. Should the further 

 description tend to substantiate the correctness of Professor von 

 Bath's observations, it is evident that some of the arguments put for- 

 ward both by the supporters and opponents of the igneous theory of 

 the origin of Quartz in modern volcanic lavas and granite, based on 

 its density, will be materially afiected. The fuller particulars will 

 be anxiously looked for. T. D. 



• 



EELIQUIiE AQUITANICiE ; BEING CONTRIBUTIONS TO THE ArCH^OLOGY 



AND Paleontology of Perigord and the adjoining Provinces 

 OF Southern France. By Edouard Lartet and Henry Christy. 

 Edited by Prof. T. Rupert Jones, F.G.S. Part Y. London : H. 

 Bailliere. 4to. Part V. April, 1868. 



IN this part the description of the Geology of the Vezere is completed 

 by a short account of the ossiferous caves and recesses. These 

 " (whether or not, in some cases, enlarged artificial^) have been 

 hollowed out by atmospheric agency, where the softer alternate with 

 the harder bands of limestones, the latter often still forming more 

 or less continuous ledges around the interior." 



With regard to the in-filling of the cavern of Le Moustier with 

 red, sandy, micaceous alluvium, very similar to the brick-earth of 

 the valley below, "it is not necessary to suppose that the cave was 

 on a level with the flood-waters of the valley since Man inhabited 

 it; for, as Mr. John Evans has suggested (Geol. Soc. Lond. June 

 22, 1864), the sand may either have been blown in by the winds, 

 or, possibly, it may have reached the cave from the top of the hill 

 during the formation of a talus, removed for the most part, since that 

 time, by the river having swept the foot of the cliff, from which it 

 has now receded." 



Some such explanation as the above is absolutely requisite in 

 cases where the valley is of very considerabh^ width, and the filling 

 in of some of the caves on the east side of Gilmiltar, partly by wind- 

 blown sand from Catalan Bay, and in part by a talus formed of dis- 





