GEOLOGY AND PALEONTOLOGY OF CANAL ZONE Norms
 [Cross-Iddings-Pirsson-Washington classification]


Q uartz __.__-_._Orthoclase _-__--A lbite -__-_-_-Anorthite _Corundum Diopside
Hypersthene Olivine M agnetite _-_-.-Ilm enite__- ..____A patite____- _____-


1


22. 26 5. 00 34. 58
24. 74 1. 22

6. 06

2. 78 .60 .31


8.
5.
44. 20.


 81 12. 63

 3. 48 2. 58 1.55


 Symbols: (1) 1.4.3.5, amadorose; (2) II.5.3.5, beerbachose; (3) tonose; (6) 1.4.3.4, yellowstonose; (8) 11.5.4.4-5, hessose.

 AGE

 The Bobio formation of the Quebrancha syncline, which is of Oligocene age, includes a thin flow of basalt. Flow breccias and minor flows are found in the Oligocene(?) Bas Obispo formation and Las Cascadas agglomerate. Coarse-grained fragmental volcanic rocks, in the form of agglomerates, make up the bulk of the Bas Obispo formation and Las Cascadas agglomerate and occur in other formations of Oligocene and early Miocene age, particularly the Caimito formation of the Gatun Lake area (Oligocene), the Oligocene part of the Caimito formation of Madden basin, and the Panama' formation (early Miocene). Altered tuff is the chief constituent of the early Miocene Cucaracha formation, which underlies the Panama' formation. The Gatuncillo formation (middle and late Eocene) and Chagres sandstone (early Pliocene) contain very little tuffaceous material, and tuff in the middle Miocene Ga tun formation is very fine-grained.
 The distribution outlined in the preceding paragraph indicates that the well-dated Tertiary volcanic rocks, including the fragmental volcaiics derived from a nearby source, are of Oligocene and early Miocene age. The volcanic centers presumably were in the area of undifferentiated volcanic rocks in the southwestern part of the area covered by plate 1 or farther west. Maiy remnants of basaltic flows in the southeastern part of the Canal Zone which are not dated, except insofar as they lie on rocks of Oligocene or early Miocene age, probably are of the same age as the better dated volcanic rocks. The fine-grained tuffaceous material in formations of earlier and younger age than Oligocene and early Miocene evidently was erupted at distant localities, probably west of the map area, where a thick


1.4.2.4, lassenose; (4) 11.5.3.5, beerbachose; (5) 111.5.3.4, campsuccession of volcanic rocks is known to be present. The thick succession of that area doubtless includes flows and intrusives younger than those of the map area.
 The intrusive Tertiary rocks are intruded into form ations ranging in age from middle and late Eocene to early Miocene. In the Gatun Lake area the Oligocene Caimito formation is intruded by basalt, but no intrusive rocks have been found in the next younger formation-the middle Miocene Gatun formation-or in the still younger Chagres sandstone. In the Gaillard Cut area and still farther southeast, the formations of early Miocene age (Culebra, Cucaracha, and Panama formations) are widely intruded by dikes, sills, and stocks. In that area, however, no Tertiary deposits younger than those just mentioned are recognized and they represent the early half of the early Miocene. If the upper limit of intrusive activity in the Gatun Lake area is applicable in the Gaillard Cut area and farther southeast, none of the intrusive rocks is younger than early Miocene. Some of them, however, may be older. The intrusive rocks, like the volcanic rocks, probably represent the period of time from Oligocene to early Miocene.
 The youngest intrusive rocks include the basalt forming dikes that extend around small hills of agglomerate in the Gaillard Cut area (Thompson, 1947a, p. 27; 1952). The agglomerate, which represents part of the Pedro Miguel agglomerate member of the Panami formation, is faulted into the underlying Cucaracha formation along a more or less circular minor fault dipping steeply toward the agglomerate. Movement along the fault may have resulted principally from plastic deformation of the bentonitic clay of the Cucaracha formation. The basalt dike is intruded


56


V


2


22 00 01 01


22. 10.
49. 9.


74 56 25
45


4


2. 40 2. 78 35. 63 21. 68

11. 19 14. 63


3. 06 2. 78 24. 10


5



8. 34 20. 96 24. 74

26. 26 3. 09 4. 75 6. 50 1.82 .93


6


20. 16 7. 78 42. 97 14. 18

 .99 1. 63

 3. 02 1.22


3. 15

2. 32 .91 1.57


4.
3.
1.


87 19
24


33.


11. 17.

4.
2.


0O

12 40,

17
43 62


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