102 STUDIES IN GEOLOGY, No. 4 



The Gamopetalae which furnish representatives of but 5 

 orders, have the three orders Gentianales, Polemoniales and 

 Rubiales fairly well represented, whereas the two orders 

 Primulales and Ebenales are scantily represented, although 

 both are important in the existing flora of the American 

 tropics. 



The order Primulales, or Myrsinales as it should be 

 called, since the Myrsinacese are much more ancient than 

 the Primulaceae, has but a single species of Ardisia in the 

 Chilean flora. This is represented by incomplete material 

 which as far as it goes is comparable to the leaves of the 

 existing Ardisia ambigua Martius of the Amazon basin. 

 The genus contains over 200 existing species and is found in 

 both the oriental and occidental tropics, and as would be 

 expected, about 20 fossil species are known from North 

 America, Europe and Asia. 



The Ebenales with 4 families and over 1,000 existing 

 species has two species of Styrax of the family Styracaceae 

 in the Chilean flora, and no traces have been discovered of 

 the families Sapotaceae or Ebenaceae the two big families of 

 the order, and both with a geological history going back to 

 Upper Cretaceous times. This is especially strange in the 

 case of the Sapotaceae which should have been present in 

 such an association as that found in the Chilean coal meas- 

 ures, and which is found fossil in the Tertiary of Bolivia as 

 well as elsewhere in South America. 



The fossil forms of Styrax are comparable with existing 

 Brazilian species. The genus has about 60 existing species 

 and a considerable number of fossil ones which serve to 

 explain the otherwise inscrutable disconnected range of the 

 modern forms. 



The order Gentianales is represented by the single family 

 Apocynaceae with 4 species in as many genera. All have 

 been compared with existing species of the Amazon basin, 

 which they closely resemble. The genus Thevetia, with few 

 species, is still confined to the region between Mexico and 



