258 J. Ro)n(mes — The Peninsula of Nicoya, Costa Rica. 



IV. — Geological Notes on the Peninsula of Xicoya, Costa IIica. 

 By James Eomanes, M.A., F.G.S. 



Contents. 



1. Introduction. 



2. Limestones and Cherts. 



3. The Igneous Eocks. 



4. The Nicoyan Series. 



o. Lithology of the Nicoyan Series. 



6. Coastal TopograiDhy. 



7. Summary and Conclusions. 



1. Introduction. 



DURING a visit to Costa llica in the year 1910 I was able to spend 

 about ten dujs in tbe comparatively little-known peninsula of 

 Nicoya. Tbe trend of the peninsula is north-west to south-east, and 

 it is separated from the mainland by the Gulf of Nicoya, a shallow 

 arm of the Pacific Ocean, whicii opens to the sea on tlie south-east. 



The country is almost unmapped, and very little has hitherto been 

 published as regards its geology, although Siiess' makes special 

 reference to it as a promising field for investigation. Sapper^ 

 traversed certain parts and records the occurrence of some rock- 

 types, but gives no detailed description whatever. 11. T. Hill,^ in 

 his paper on the Geological History of the Isthmus of Panama, 

 mentions that Sjogren spent some time in Nicoya, and tbat his results 

 are to be found in an appendix to the paper. No such appendix has, 

 however, been published, and I have been unable to find any account 

 of Nicoya by that author. 



I spent some days in the village of Nicoya, Avhich is situated almost 

 in the centre of the peninsula, and then made a journey to the south, 

 getting as far as the Rio de Ora. The area is one of higli relief, and 

 range after range of hills is encountered in travelling through it. 

 In certain parts, however, there are broad tracts of level country from 

 which the hills rise abruptly, and reference to this feature will be 

 made in a subsequent part of the present paper. In some respects 

 Nicoya shows close geological affinities with the adjacent portion 

 of the mainland described by the present writer,* while in others 

 it affords a striking contrast. 



In such accounts as liave been previously published there seems 

 to exist a strong impression that older metamorphic rocks contribute 

 largely to the formation of this portion of Costa Rica, but so far as my 

 observations go this is entirely without foundation. It is only fair, 

 however, to point out that this paper is the result of what really 

 amounts to a single traverse from north to south, so that plenty of 

 room remains for the existence of metamorphic rocks; yet throughout 

 all the part Avith which I am acquainted the geology shows such 



^ The Face of tlie Earth, vol. iv, pt. v, p. 459. 



- " Ueber Gebirgsbau und Boden des siidlichen Mittelamerika " : Peterm. 

 Mitth. Erganzungsb., xxiii, No. 151, pp. 26-7, 1906. 



'^ " The Geological History of the Isthmus of Panama and portions of Costa 

 Eica" : Bull. Mus. Comp. Zool. Harvard, vol. xxviii, p. 222, 1898. 



^ Quart. Journ. Geol. Soc, vol. Ixviii, pp. 123-33, 1912. 



