Vol. 68.] GEOLOGY OF COSTA KICA. 109 



The best development of the sandstone is seen along the road 

 that winds up the hills from the village of El Higuito, a few miles 

 to the west of San Miguel. Just above El Higuito, at a height of 

 about 4000 feet above sea-level, sandstone begins to be exposed 

 along the roadside ; this is exactly similar to some of the Patara 

 deposit. It is a fine-grained friable sandstone with an extra- 

 ordinary range of bright colours — white, yellow, red, and brown 

 being the commonest. The colouring imparts to the rock a ver}" 

 mottled and banded appearance and the colour-banding often 

 shows a distinctly concentric form, corresponding with the type 

 of weathering described by Mr. Hayes in Nicaragua,^ and this has 

 generally masked completely any bedding which may have origin- 

 ally been present. When the least evidence of bedding is visible, 

 the beds appear to be highly contorted. 



The sandstone is chiefly formed of extremely angular fragments 

 of quartz, many of which show fresh fractures and no trace of 

 subsequent rounding ; along with the quartz-grains are fragments 

 of felspar and devitrified volcanic glass. The cement is a red 

 oxide of iron. This rock, while of undoubted marine origin, 

 stl'ongly suggests that deposition has been rapid, and that explosive 

 volcanic action has taken part in the preparation of the material. 



At an altitude of about 4500 feet a thin dark band of car- 

 bonaceous shale is interstratified with the sandstone. This band 

 contains some very fragmentary plant-remains, and strikes north 

 70° east, dipping 70° south-eastwards. At a height of 5300 feet is 

 a good cliff-exposure by the roadside ; here the rock has rather a 

 different character, resembling nothing so much as a badly-burnt 

 gault-brick, with much brown iron-staining along the joint-faces. 

 This exposure has yielded some fossils, namely, casts of Pecten. 

 The species is much smaller than that from the 8an Miguel Lime- 

 stone, measuring only about 3 inches across. Still higher, at 

 5500 feet, occurs a much-jointed band of very fine, compact, dark 

 grit, about 50 feet thick. 



In a small stream a short distance below this, I found a frag- 

 ment of this rock on which was the cast of a small Pecten. Erom 

 this point right up to the watershed (6300 feet) the only rock 

 exposed in place is the sandstone, with the exception of a very 

 decomposed greenish tuff at the altitude of 5800 feet, which 

 appeared to be horizontally bedded. 



The sandstone is thus continuously exposed on this road through 

 a vertical height of some 2300 feet ; but it is, of course, quite 

 impossible to give any estimate of its true thickness. A remark- 

 able feature of this traverse is that not a trace of the San Miguel 

 Limestone is encountered, and I was unable to obtain any evidence 

 as to where its outcrop lies west of Patara. 



Passing now to Tres Eios, somewhat similar deposits are seen 

 in the roadside sections below the limestone-quarries. Immediately 



^ 0. W. Hayes, EuU. Geol. Soc. Amer. vol. x (1899) p. 325. 



