220 Washington — Catalan Volcanoes and their Bocks. 



these upon the preexisting topography was comparatively slight, 

 and consisted largely in the building up of cinder cones and 

 the tilling of the river valleys by lava flows, resulting in the 

 formation of some lakes and marshes. But, on the whole, the 

 preexistent drainage persisted, and the rivers now follow their 

 old courses, having cut new channels either through or along- 

 side of the lava flows, coming out into their old beds when the 

 lava ends. Excellent illustrations of this are to be seen in the 

 valleys of the Fluvia and of the Amer ; in the latter case the 

 relations of the lava flow to the old drainage, and the abrupt 

 end of the former being especially well seen from the railroad, 

 a few kilometers below Las Planas. 



The Lava Flows. — The igneous ejections are readily refer- 

 able to two distinct periods, a separate type of eruption dis- 

 tinguishing each. The earlier seem to have been uniformly 

 quiet, and formed extensive flows of basalt, which poured out 

 into the river valleys and other depressions as explained above. 

 The points of origin of most of these are not readily made out 

 and are somewhat problematical, owing to their subsequent 

 burial beneath later ejections and recent deposits. But in 

 general they seem to have issued from at or near the sites of 

 scoria cones now in existence. These flows, of which Gelabert 

 enumerates ten principal ones, varied in length from 5 to 15 

 kilometers, and seem to have been uniformly quite thick, up to 

 40 or 50 meters. Of these the most important are : one which 

 issued from near Santa Margarita and flowed northeasterly 

 down the valley of the Rio Cor, past Santa Pau and Sellent, a 

 distance of about 10 kilometers ; a second which issued from 

 near La Garrinada and flowed easterly down the valley of the 

 Fluvia past Puig Estany and Baguda as far as Castellfullit, a 

 columnar structure being especially well developed in this ; a 

 third which flowed from near Bana de Boch down the valley 

 of the Riera de Llemana as far as the chapel of Sant Medir 

 near Llor&; and a fourth which issued from near the Puig 

 Montcal at Adri and flowed southeasterly as far as Domeny, 

 near Gerona, a distance of about 12 kilometers. 



Partially filling the preexisting river valleys, these flows pre- 

 sent a characteristic feature of the topography, and when they 

 have been cut into by subsequent river erosion, or where the 

 river has cut for itself a channel between the lava and the 

 adjacent limestone, highly typical and very striking illustra- 

 tions of columnar structure are revealed. Of these the best 

 known is that at Castellfullit, which has been described by 

 almost every writer who has visited the region. The flow 

 here is about 50 meters thick, and forms a precipitous tongue 

 of dark gray, prismatic lava, crested with the little village 

 above, and with the turbulent stream below. The upper half 



