E. E. L. Dixon — The Gavarnie Overthriist. 359 



the calyx + wings is greatest just below the level of the radial 

 articular surfaces, and is approximately equal to the length ; it 

 diminishes rapidly towards the base. 



The interior of the calyx is deep, and is hounded by the five 

 compound interradial spines (Figs. 1, 2, i.s.). These are slightly 

 concave internally, whilst externally they bear two deep grooves, 

 separated by a median carina (Figs. 1, 2, c). The spines are very long, 

 being more than half the length of the calyx ; they have only a slight 

 inclination outwards, and consequently the angle between two adjacent 

 spines is small. 



The wings of the radials are visible in an oral view (Fig. 1), and give 

 a characteristic pointed appearance to the external margins of the 

 radial articular facets (Fig. 1, ar.). The latter are nearly horizontal, 

 and lie outside the ring of interradial spines. Each bears a distinct 

 external ligament fossa (/.), below the general level of the facet and 

 a central axial canal (Fig. \, ax.). Basals five, oval, situated more than 

 half-way up the calyx (Fig. 2, h.). Tegmen, arms, and stem unknown. 



Roveacrim<,s communis, sp. nov. (PL XVII, Figs. 3, 4.) 

 In this form the radial flanges are not visible in an oral view ; the 

 external margins of the articular surfaces are straight, and consequently 

 the "calyx appears pentagonal. Calyx long, narrow, funnel-shaped. 

 The radial flanges are in the form of rounded keels, bifurcating below 

 the articular 'facet, but produced downwards into single cylindrical 

 projections. The radial articular facet has a slight outward 

 inclination and shows a distinct central axial canal; the interradial 

 projecti6ns are shorter and more widely divergent than in R. alata. 

 Basals indistinctly marked, situated at a greater distance from the 

 radial articular facets than in R. alata. Tegmen, arms, and stem 

 unknown . 



- R. communis, var. rugosa, var. nov. (PI. XVII, Fig. 5.) 

 In one specimen, which I regard as a varietj^ of R. communis, the 

 radial flanges are partially obliterated by regular nodular thickening, 

 which gives the aboral surface of the calyx a rugose appearance. The 

 articulation for the stem is distinctly visible and appears to be circular. 

 The specimens figured are from Dr. Eowe's collection from 

 Seaford Hetjid, Sussex. 



VJI. — The Gavaenie Overtheust, and other Pkoblems in Ptrenean 



Geology. 



By E. E. L. Dixon, B.Sc, F.G.S. 



(PLATE XVIII.) 



IN view of the interest which cTiarriages and extensive overthrusts 

 of low inclination are exciting in various parts of the world, an 

 interest which has steadily increased since Mcol first put forward his 

 explanation of the anomalous position of the Moine gneisses, it may 

 be worth while to place before readers of the Geological Magazine 

 a brief account of a remarkable structure in the Pyrenees, which has 

 been noticed by various geologists, but only recently explained, by 



