io8 STUDIES IN GEOLOGY, No. i 



Maximum width, at or above the middle, 4 mm. to 7 mm. 

 Petiole stout, often curved, 3 mm. to 6 mm. in length. 

 Midrib stout, prominent on the under side of the leaf, 

 usually curved. Secondaries thin, numerous, diverging 

 from the midrib at wide angles, rather straight, ultimately 

 camptodrome. The secondaries are immersed in the thick 

 substance of the leaf and are entirely obsolete in the 

 leaves preserved in the relatively coarse matrix at Coro- 

 coro, but better displayed in the material preserved in 

 the fine textured Potosi tuff. The tertiaries are largely 

 obsolete by immersion, although the characteristic Dodo- 

 naea areolation can be made out in the material of this 

 species collected at Potosi. 



This species is exceedingly abundant in the lower 

 plant-bearing stratum at Corocoro but is less common at 

 Potosi. It is on the whole well marked and is strikingly 

 similar to the existing Dodontea tiscosa Linne, especially 

 the smaller leaves of that species. The latter is found 

 in both the oriental and occidental tropics and is a char- 

 acteristic insolation resisting form of the strand and coastal 

 lagoons. It ranges northward to peninsular Florida and 

 Bermuda (32 North) in this habitat and is also found 

 in the interior of South America. According to Weber- 

 baiter it occurs in the Andean valleys of Peru at altitudes 

 up to 9750 feet. Farther south I found it east of the 

 divide of the Cordillera Oriental north of Misque at an 

 altitude of 8450 feet, where it was exceedingly common 

 in bush form and abundantly fruiting at the end of the 

 dry season. (Sept. I, 1919) 



The genus Dodonaea has perhaps 50 existing species, 

 the majority of which are Australian, but it is represented 

 in all tropics and is a member of the Hawaiian flora. Its 

 cosmopolitan distribution denotes an extended geological 

 history, in confirmation of which it has been discovered 

 in the lower, middle, and upper Eocene of the Mississippi 

 embayment region, where it is represented by both leaves 

 and the characteristics alate fruits. There are over a 



