Vol. 68.] GEOLOGY OF COSTA EICA. 131 



complex form allied to Tinoporus} The other fossils are extremely 

 badly preserved, being mainly much- crushed fragments of small 

 gasteropods and lamellibranchs. 



As regards the source of the material that forms the Manzanilla 

 Series, it is difficult to base any definite conclusion on the rather 

 scanty evidence at present available. Even the data collected 

 give rise to contradictory evidence : on the one hand, the purely 

 volcanic nature of the material and the angularity of the fragments 

 in the deposits at Las Juntas suggest that here we are close to 

 the volcanoes which gave rise to the deposits : in support of this 

 must be taken into account the fossiliferous nature of the deposits 

 at Manzanilla, the evidence which they give of considerable rounding 

 by water-action, and the admixture of non-volcanic material. On 

 the other hand, the apparent increase of coarseness of the material 

 as we trace the beds westwards from Las Juntas seems to point to 

 the source of the material having lain to the west. On the whole, 

 I am of opinion that the material has not been derived from a 

 simple source, but has been fed in from many different directions 

 and that the conglomerates are a local facies dependent on the 

 proximity of large, or at least torrential, streams. 



The Manzanilla Series appears to correspond very closely with the 

 Brito Series described by Mr. Hayes ^ from Nicaragua. According 

 to this author, the material forming the Brito Series was derived 

 from some volcanic range lying to the west of the present Pacific 

 shore-line ; such a range of mountains may well have supplied much 

 of the material now forming the Manzanilla Series. Although, 

 as yet, no direct palseontological evidence can be given as to the age 

 of this series, the great similarity of many of the rock-types to 

 those described at Barranca and their similar mode of occurrence 

 make it more than likely that they will eventually prove to be 

 contemporaneous. 



The geology in this area seems to indicate three distinct periods 

 of movement, and its history must have been more or less as 

 follows : — 



(1) Uplift of the older limestones. 



(2) Denudation of these and formation of the Manzanilla Series. 



(3) Uplift and folding of the Manzanilla Series. 



(4) Base-levelling of the folded beds. 



(5) Final uplift of a few hundred feet, initiating the raised coastal 



peneplain. 



(c) Gulf of Nicoya. 



The Gulf of Nicoya is a large stretch of very shallow water which 

 extends from north-west to south-east, opening into the sea in the 

 latter direction. On the north-east it is bounded by the mainland 

 of Costa itica, and on the south-west by the peninsula of Nicoya. 



^ Dr. E. L. Sherlock has very kindly examined some of the slides, and informs 

 me that this foraminifer is most probablv a species of Orhitoides. 

 2 Bull. Geol. Soc. Amer. vol. x (1899) "p. 309. 



