30 STUDIES IN GEOLOGY, No. 3 



represents, faunally, a later stage, and that the appearance 

 in further collecting of a reasonable number of more modern 



species would easily throw the balance toward the Helvetien. 



As was noted in the preceding discussion of formational 

 inter-relationships, the Areas and the Turritellas are the 

 chief distinctive groups of the Upper ZorritO'S, and although 

 some of the species range into the Variegated, their complete 

 difference in the Lower Zorritos affords one point of dis- 

 tinction between the two formations which may prove of 

 use in field recognition. Other species, such as Pecten 

 woodringi, Conus cacuminatus, and Cerithium infrano datum, 

 of the Upper Zorritos ; Dosinia grandis, Corbula propinqua, 

 and Macrocallista helenae, of the Variegated ; and a much 

 larger number from the Lower Zorritos appear to be char- 

 acteristic, and may serve similar purpose ; however, they 



- are as a whole not as prominent as the Areas and Turritellas, 

 and their range is not yet sufficiently well known to make 

 them of high value. 



Variegated Fauna: The collection from the Variegated 

 beds, of fifteen species, is too small to permit far-reaching 

 conclusions, but a few observations may be worth while. 

 The preponderance of Burdigalian elements, well over half 

 the total, in the fauna here represented is such as leave small 

 doubt as to the age of the beds, and although the general 

 facies is in some ways similar to that of the Upper Zorritos 

 fauna, the affinities are closer to those of the Lower Zorritos. 

 That fact .lends strength to the possibility that the whole 

 formation is of nearly the same age, but it can not mean much 

 at present ; future work might easily change the conclusions 

 based on so small a faunule as that now available. There is 

 small doubt, however that the Variegated will prove to be of 

 Burdigalien age. 



Grzybowski lists 16 species from the Variegated (his 

 Heath), of which only three occur in the present collection, 

 with none of the three from the Variegated. The remaining 



