222 A. M. Finlauyson—Petrology of Huelva, Spain. 
with the upper members of the crystalline series, and are widely 
developed in the adjoining provinces of Badajoz and Cordoba. A belt 
of undoubted Silurian rocks, unconformable to the Cambrian, also 
occurs in the northern district. In these have been found graptolites, 
including Donograptus Nilsson (Barr.), IL. latus (McCoy), IL. linnei 
(Barr.), and IM. convolutus (Hisinger),’ as well as the so-called nereites,” 
identical with forms found in the French Pyrenees.? 
In the slates of the mining belt to the south, similar nereites were 
found at Santo Domingo Mine in Portugal, at Lagunazo near Tharsis, 
and elsewhere. On this basis, on supposed lithological differences, 
and on the results of the researches of J. F. N. Delgado in Portugal,* 
a large area of the slates of the mineral zone was mapped as Silurian 
by the Spanish Survey. The rocks, however, contain no graptolites 
like those in the north, the lithological differences are insufficient to 
be of any value, and no unconformity can be detected between these 
rocks and the Carboniferous strata which compose the rest of the 
district. Further, since that date, the belief that the so-called nereites 
represent true fossils has been much discounted, and it is noteworthy 
that Delgado now places the nereite-bearing phyllites of Portugal in 
the Devonian.® Finally, the writer obtained a number of well- 
preserved specimens of Posidonomya bechert, the fossil found in 
the rocks of the district which are mapped as Carboniferous, in 
so-called Silurian rocks at the mine of Cabezas del Pasto, in Huelva, 
near the Portuguese border. All the evidence available, therefore, 
tends to show that the rocks throughout the mining district belong 
only to one period. 
These rocks in general are quartz schists, phyllites, and thin- 
bedded slates, with bands of greywacke and quartzite, and, more 
rarely, limestones. A rapid alternation of greywackes and slates is 
frequently seen, as in the west of the province, at La Laja on the 
Guadiana, and in the Tharsis district. The strike of this sedimentary 
series is remarkably uniform throughout the field, approximating to 
W. 15° N. The rocks generally dip, at a varying angle, towards the 
north. They are fossiliferous at several localities round Rio Tinto, 
the slates near the Marismilla dam on the road to Nerva, and also 
adjoining the Bessemer plant, yielding good fossils. The following 
forms have been described by Lucas Mallada*: Goncatites sphericus, 
Posidonomya becheri, P. lateralis, P. gonzaloi, P. edmondia(?), P. con- 
stricta, P. barroisi, and others. Several of these species, including. 
1 Gonzalo y Tarin, loc. cit. sup., vol. i, p. 405. 2 Thid., p. 395. 
3 Ch. Barrois, ‘‘ Sur les ardoises a néreites de Bourg d’Oueil (Hte.-Garonne) ”’ : 
Ann. Soc. Géol. du Nord, 1884, vol. xi, p. 219. 
4 J. F. N. Delgado, ‘‘ Sobre a existencia do terreno siluriano no Baixo Alemtejo”’ : 
Jorn. Sci. Math. Phys. e Nat., Lisbon, 1878, vol. v, pt. ii; and ‘‘ Correspondance 
relative la classification des schistes siluriens 4 néreites découverts dans le sud du 
Portugal’’: ibid., 1880, vol. vii, p. 103. 
5 J. F. N. Delgado, ‘‘ Systeme silurique du Portugal’’: Commission du Service 
Géologique du Portugal, Lisbon, 1908, pp. 10 and 223. J. F. N. Delgado and 
P. Choffat, ‘‘ La carte géologique du Portugal’’: Congrés Géol. Internat., sess. viii, 
1900; Paris, 1901, p. 743. 
6 « Descripcion fisica, geologica, y minera de la provincia de Huelva’’: Mem. 
Com. Map. Geol. Esp., 1886, vol. i, p. 663. 
