226 BULLETIN: MUSEUM OF COMPARATIVE ZOOLOGY. 



country there can be seen evidences of terraces which, if properly studied, 

 could be interpreted into an interesting geologic history. The beautiful 

 suburb of San Jose, known as the Savanna, is a small flat area composed 

 of lacustral alluvial soil, and so level that it looks as if the waters had 

 only been recently withdrawn from it. In no instance is there any 

 body of water now retained in the lower levels of these aucient lake 



^m^.<m^^^<m 



Figure 23. Section of Boulder Clays, Flank of Irazu Summit, 

 between San Jose and Cartago (Gabb). 



beds, for the modern drainage has and is now cutting deep canons into 

 them far below the last lacustral occupation. These streams reveal in 

 their canons and gorges the same red clays and igneous boulders so 

 characteristic of the older igneous foundation encountered upon the 

 Pacific coast. In addition there are many outcrops of massive black 

 igneous rocks. The accompanying illustrations give a characteristic 

 picture of the boulder topography of the lowest drainage cuts in the 

 central basin (Plate XIV.). 



The San Miguel Beds. — On the south side of the east and west chain 

 of bolsou valleys, and standiug parallel with and opposite the volcanic 

 heights forming their northern border, there is another large range of 

 mountains running east and west, known as the Sierra Candella. Al- 

 though there is no mention of limestone formations in Costa Rica, I was 

 informed that the lime used in the city was burned from the stone found 

 in the base of these mountains. I visited the site of the kilns, some 

 three leagues south of San Jose, near the villages of San Miguel and 

 Desamparado. The road the whole distance ascends about 400 feet 

 above the city through the volcanic tuffs, including some of the later 

 and whiter volcanic rocks that I had not seen elsewhere until we reach 

 the foothills of the mountains. This I found to be composed almost 

 entirely of a massive blue-black Paleozoic looking limestone which was 

 being quarried at several places. The strata were much disturbed, dips 

 being found in many directions, but so concealed by the vegetation that 

 it was impossible to make out any systematic arrangement. The only 

 conspicuous fossils that we could find after much search was a very large 





