636 Arnold Heim — 



" PURISIMA NUEVA FORMATION." 



The only locality where this formation so far has been encountered 

 is situated on the west side of the beautiful oasis La Purisima nueva 

 (Lat. 26° 11', Long. 112° 4'), where the Purisima River or Arroyo 

 Cadegomo has cut out three small anticlinal " windows ". In 

 a previous paper on the volcanoes of La Purisima, in 1921, the 

 writer has mapped these outcrops under the name of " Purisima 

 Nueva Formation ". 



The rocks are composed chiefly of light-coloured to white sand- 

 stones with beds of broken shells (lumachelle). They are intensely 

 compressed and folded, and thereby partly marmorized. 



From the eastern outcrop, just at the western end of the date 

 palms on the foot of the southern Mesa, fossils were found, among 

 which are beautifully preserved Echinids. 



The middle outcrop in places is very fossiliferous. Well preserved 

 Pecten, Turritella, Balanus, etc., were collected on the river banks, 

 in a straight distance of 38 kilometres west of the old Mission of 

 La Purisima Nueva. The dip of the strata here is 70° to the west. 



In an abstract of a paper by Dr. Ralph Arnold and Professor 

 Bruce L. Clark,^ the following statement is made : — 

 " Certain of the species are common to the Apalachicola horizon 

 at a number of localities around the Caribbean Sea." 



" Pecten condylomatus Dall is found in the Chattahoochee and 

 Chipola beds of Florida and, according to Dr. R. E. Dickerson, 

 is present also in the Tuxpan beds of Mexico. 



" Pecten oxygonum optimum Brown and Pilsbry is common in 

 the Gatun beds at Panama. 



" Raeta gibbosa Gabb was described from the Peruvian Tertiary, 

 and is also found, according to Dr. Dickerson, in the Miocene of 

 the U.S. of Colombia, the fauna of which is considered by him to 

 be a phase of the Gatun fauna. 



" Mactra dariensis Dall is found in the Gatun beds. 



" Turritella tristis Brown was described from the Miocene of 

 Costa Rica." 



" The recognition of this fauna in Lower California is important 

 in that it apparently indicates a direct connexion between the 

 Pacific and Atlantic oceans somewhere in the region of Central 

 America during the Apalachicola period of deposition." 



In another abstract, by R. E. Dickerson, ^ the same fossils are 

 cited. Dr. Dickerson considers them equivalent to the Bowden 

 fauna of the Antilles. The following quotation is taken from his 

 paper : — 



" The rest of this fauna contains casts of forms which represent 

 typical Bowden genera. The fauna, beyond doubt, is some phase 



^ Ralph Arnold and Bruce L. Clark, " An Apalachicola Fauna from Lower 

 California," Bull. Geol. Soc. America, vol. xxviii, 1917, p. 223. 



^ R.. E. Dickerson, " Ancient Panama Straits," Bull. Geol. Soc. America, 

 vol. xxviii, 1917, p. 230. 



