200 bulletin: museum of comparative zoology. 



from the outcrops I saw just above its base, but from all the other 

 mountains of the central igneous region. 



I endeavored to ascertain the geologic structure of Cerro Ancon, but 

 owing to the dense vegetation and residual soil no exposures of bed rock 

 could be found, except at the Canal Company's hospital on the north side 

 aud along the water front upon the south. At both localities outcrops 

 extend to about 100 feet above the base of the mountain. The only 

 rocks exposed were highly disturbed stratified material of greenish white 

 color which is later described as the Panama formation. Neither Maack 

 nor other explorers have succeeded in ascertaining the material compos- 

 ing the higher slopes of the mountain. 



T7ie Panama Formation. — A formation analogous to the beds at 

 Miraflores occurs along the Pacific coast in the city of Panama and in 

 the adjacent islands. At Panama it constitutes the steep bluff at the 

 water front, as well as the strip of land extending eastward toward the 

 mouth of the canal at the foot of Cerro Ancon. This same rock also 

 outcrops upon the island of Naos, four miles out in Panama Bay. 



The geologic composition of the material at Panama is a greenish 

 white stratified fine grained material resembling sandstone with occa- 

 sional beds of conglomerate. These beds are quite strongly flexed, 

 similarly to those at Miraflores, indicating that they have undergone 

 considerable disturbance since their original deposition. No traces of 

 fossils could be found, nor other evidence affording the least indication 

 of the age of this material, or its relation to the other sedimentaries. 

 Maack 1 has described the material of the Panama formation, and Mr. 

 Garella 2 also noted it. 



The specimens collected by the writer from this peculiar formation 

 were submitted to both Professor Wolff and Mr. Turner for determina- 

 tion. Mr. Turner says concerning it : — 



" The specimen No. 45, from the Panama Cemetery Gate, is of volcanic 

 origin. The rock has a micro-crystalline feldspathic groundmass in which arc- 

 embedded abundant broken feldspars, with a few showing idiomorphic out- 

 lines. Many of the feldspars are twinned on the albite law, and as their index 

 of refraction is less than that of the balsam, these twinned feldspars are albite. 

 No original meta-silicates were seen, but there are patches and spots of a green 

 secondary pleochroic substance, probably in part chlorite, in one patch of which 



1 Op. cit., page 164. 



- I'roject of a Canal to connect the Atlantic and Pacific Oceans across the 

 Isthmus of Panama, by Napoleon Garella, Engineer in Chief of the Royal Corps of 

 Miners. Rep. No. 145, D. S. House Rep., February 20, 1849, page 520. 



