J. Romanes — The Peninmla of Nicoya, Coda Rica. 263 



To pass now to another part of the peninsula, the same sedimentary 

 series is well exposed along the Pacific coast from the E.io Buenavista 

 to the Kio de Ora. Here the topography is somewhat different as 

 hills and valleys alternate without the broad plains which, characterize 

 the land to the north. The sediments extend inland for some distance, 

 but to judge by the river gravels igneous rocks occupy most of the 

 interior. 



Buenavista Bay is bounded at either end by a bold rocky headland, 

 and between these stretches a great curving beach of sand. The rock 

 of the eastern headland is very fine-grained, grey in colour, hard 

 and compact, with much calcite veining. The strike is E. 15° S. with 

 a southerly dip of 65°. Similar rocks form the western limit of the 

 bay, but the strike there is JS^. and S. with a very variable dip to the 

 west. A.t Samara Point, some distance to the south, the deposits are 

 much coarser in texture and show in hand-specimens numerous rock 

 fragments ; the strike is E. 20° S. with a southerly dip of 75°. The 

 farthest south that I reached was the E.io de Ora, and here again this 

 series is seen. 



5. LiTHOLOGY OF THE iS^ICOYAJJ- SeRIES. 



As previously stated these rocks show a very considerable range in 

 texture and appearance ; the coarser varieties closely resemble some 

 of the beds of the Manzanilla Series, and are evidently marine volcanic 

 ashes with, however, a considerable admixture of non- volcanic material. 

 An example from the Eio Marote may be taken as typical of these. 

 In the hand-specimen the rock has the general appearance of a coarse, 

 compact, dark sandstone, with numerous slightly rounded rock 

 fragments. Under the microscope this rock [9674] yields much 

 valuable information. It is a sli<>htly calcareous ash or fine breccia 

 similar to that figured by the present writer from the mainland.^ 



Among the rock fragments are Eadiolarian cherts identical with 

 those to be found in place a short distance further up the valley. 

 Limestone is present similar to the limestone exposed further to the 

 north and described earlier in this paper. Together with these are 

 fragments of a globigerine mudstone and small pieces of basic igneous 

 rock, not unlike the variolitic basalts of the surrounding hills. The 

 mineral particles consist of angular quartz, much fresh plagioclase, 

 green hornblende and augite, with here and there a little glauconite. 

 The cement is principally calcareous, but the amount present varies 

 greatly in different examples. A specimen [9675] from the river 

 bed at La Colonia is much finer in texture than the above, and 

 contains scattered fragments of analcime. It is therefore, I think, 

 a perfectly safe conclusion to consider the Mcoyan Series as having 

 been laid down while the older limestones, cherts, and igneous rocks 

 were being denuded and probably in many cases being broken up by 

 outbursts of volcanic activity. In these deposits are preserved Rotaline 

 Eoraminifera, Glohigerina, and fragments of the same Orhiioides that 

 characterizes the Manzanilla Series, to which I have ascribed a probable 

 Miocene age. The two series are therefore shown to be identical both 

 lithologically and palaeontologically. 



' Q.J.G.S., vol. Ixviii, pi. ix, fig. 4, 1912. 



