128 



ME. J. EOMANES OK THE 



[Feb. 191 2, 



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of the nature of shallow intrusions than actual surface lava-flows. 

 At Las Juntas the strike of these beds is 

 south 70° east, with a very gentle dip (5°) 

 eastwards. They are all very pale, white 

 or grey, and very well bedded, the bedding- 

 planes in most cases being only a few inches 

 apart. They vary considerably in texture, 

 the finer bands having the appearance of a 

 white marl, while in the coarser varieties 

 they are somewhat like a medium-grained 

 friable sandstone. In this district these 

 stratified rocks consist almost entirely of 

 [7 volcanic debris, without any trace of organic 

 =^^ remains. The coarser bands are formed 

 S principally of broken crystals of a very 

 ^ fresh labradorite, which shows the usual 

 I zonary banding. A few crystals of green 

 Jn hornblende and colourless augite are present, 

 \ together with numerous dark-green frag- 

 I raents, apparently of hornblende altered lo 

 ^ chlorite. In places are small pieces of tlic 

 I cherty material which occurs so plentifully 

 "1 in the ashes of Barranca, while pyrites and 

 H magnetite are plentiful. The ground-mass 

 § of the ash consists of minute fragments of 

 ^ the above minerals and glass ; but some- 

 I times a considerable quantity of calcium 

 S carbonate has come in, forming a more or 

 ^ less calcareous matrix. The lithological 

 I character of the finer bands is almost iden- 

 "„ tical with that of the coarser varieties, but 

 D calcareous matter is entirely absent. 



1 Eefore proceeding to a consideration of 

 H the coastal belt, a brief description of the 



2 topography is necessary. The country im- 

 5 mediately round the Avangares mines is 

 l[ typical Costa Eican mountain-scenery. The 

 ^ rivers flow in deep valleys with steep sides, 



from which rise high precipitous mountains, 

 all clothed with rich vegetation ; on these 

 slopes landslides play a very important part 

 in aiding denudation. 



Standing on the higher ground above the 

 mines, and looking south-westwards to the 

 Gulf of Nicoya, the observer sees the lower 

 slopes of the volcanic hills in the fore- 

 ground ; beyond is a broad level plain, the 

 general surface of which is 150 to 200 feet 

 A very striking feature of this landscape is the 



'C5-> 



above sea-level. 



