GEOLOGY AND GEOLOGIC HISTORY. 69 



At an altitude of 53 meters (by barometer) above the river a bed of 

 large Teredo tubes similar to Teredo incrassatus (Gabb) was crossed on the 

 east side of Rio Cana. This bed may correspond to that noted by Maury 1 

 on the river 3 kilometers below Caimito. 



The section above described corresponds to Maury's Zone H. 2 Mol- 

 lusks characteristic of the Cercado formation were also collected by the 

 Maury expedition farther upstream, at a locality apparently about 3 kilo- 

 meters above the crossing of the road from Las Caobas to Sabaneta. This 

 locality is Maury's Zone I. 3 



The Cercado formation is exposed on Rio Gurabo between Rio Mao and 

 Rio Cana, about 8.5 kilometers above Gurabo Adentro (see PL XI, stations 

 8737, 8738, 8739). The fossils from these localities are listed on pages 

 115-124, 127-129. 



The Cercado formation has been recognized as far eastward as Rio 

 Albano (station 8729), near San Jose de las Matas, where a characteristic 

 faunule, which is listed on pages 116-124, was collected. 



GURABO FORMATION. 



The type locality of the Gurabo formation is on Rio Gurabo from "Zone 

 A" to "Zone F," inclusive, of Maury, 4 near Los Quemados. As the de- 

 scriptions of localities given by Doctor Maury are obscure it is rather 

 difficult to identify some of the places she mentions. Apparently the lo- 

 cality to which she attached the name "Los Quemados" is the last crossing 

 of Rio Gurabo on the trail from Gurabo Adentro to Los Quemados, about 

 3 kilometers west of Los Quemados. (See PL XI.) The exposures on 

 Rio Gurabo are described by her in the section below. The lettered "zones" 

 are the successive bluffs met on ascending the river. 



Section at Los Quemados. 



Concealed by vegetation and unexplored. Feet. 



Limestone with poorly preserved corals. Approximate thickness 50 



Zone A. Hard light-blue clays forming vertical cliffs, slightly concave 

 near the base. The clays weather yellowish white. Fossils rare or 

 absent in the upper part of the bluffs; abundant below. Fauna 

 chiefly Gastropods. A few pelecypods, such as Venericardia and 

 Echinochama. Approximately 300 



Zone B. Hard blue clays, blocky, not well stratified, weathering 

 grayish. Fossils abundant. Thickness about 50 



Zone C. Alternating clays and limestones, with a rather heavy bed of 

 the latter above. Fossils very scarce; Cassis sulcifera. Thickness 

 approximately 10 



Zone D. Hard blue calcareous clays. Corals. Cerithium abundant. 

 About 15 



Zone E. Blue uniform clays with Cerithium, Phos, Cypraea. Ap- 

 proximately 20 



1 Maury, C. J., Am. Paleont. Bull., vol. 5, p. 441, 1917. 



2 Maury, op. cit. 



» Maury, op. cit., p. 442. 



< Maury, C. J., Science, new aer.. vol. 50, p. 591, 1919; Am. Paleont. Bull., vol. 5, p. 434, 1917. 



