GEOLOGY AND PALEONTOLOGY OP THE CANAL ZONE. 535 



Section along east side of Gaillard Cut from Canal Commission stations 184$ to 1850. 



Oligocene : 



Cucuracha formation — F e3t thick. 



11. Material the same as No. 9. Exposed 504- 



10. Bed of fairly fine gravel, loosely cemented with cal- 

 careous material. Estimated 15 



9. Light green, fine-grained, soft and friable argillaceous 

 rock. Lower part of the Cucuracha formation. 



Estimated 50 



Culebra formation — 



8. Beds of partly consolidated gravel, with some dark- 

 gray, granular, tufaceous material; light-colored, 

 limy cement. Marks a small unconformity between 

 the upper part of the Culebra formation and the 



overlying Cucuracha formation. Estimated 30 



6011-7. Limy bed similar to No. 5; contains Eeterosteginoides 



panamensis 5 



6. Material similar to No. 4. Estimated 50 



5. Fairly hard, somewhat coarse-grained, light-colored, 



sandy limestone grading into limy sandstone 5 



4. Dark-gray, thin-bedded, friable tufaceous beds with 

 partings of soft dark carbonaceous shales. Part of 

 upper part of the Culebra and practically same as 



(2). Estimated 50 



3. Two beds of gravel loosely cemented by light-colored 

 limy cement. A 3-foot bed of dark, friable, car- 

 bonaceous shale separates the two gravel beds. 

 Gravel contains a* number of oysters and seme other 

 fossils. Appears to be a local unconformity here. 

 Estimated thickness of gravel beds, including the 



shale bed 30 



2. Thin-bedded, granular, and somewhat friable, dark- 

 gray, tufaceous sandstone beds, separated by soft, 

 dark-brown, carbonaceous shale layers; a few peb- 

 bles present. Part of the upper part of the Culebra 

 formation. Dip about 35° northward. Estimated. 100 

 Age? 



1. Laccolithic mass of basalt which has tilted the beds into 

 which it was intruded and slightly metamorphosed them 

 for a foot or more distant from the contact. A dike 1 to 3 

 feet wide seems to connect with main mass. 



Section on west side of Gaillard Cut from Canal Commission stations 1775 to 1756. 



Section shows three small faults, also contact between Cucuracha forma- 

 tion on top and Culebra formation beneath it. Thickness of entire 

 section 4004- feet. 

 Oligocene : 



Cucuracha formation — ■ 



2. Fine-grained, light-green, fairly massive volcanic clay 



rock. Fe&t thick. 



/. Same as (d) 100 



e. Andesite-breccia flow. About 20 



d. Light-green, fairly massive, volcanic clay rock 3 to 8 



c. Small lens of limy sandstone. Maximum thick- 

 ness about 1 



