724 



JAMES H. GARDNER 



The third member above the base of the Puerco in the above 

 section is a very persistent horizon-marker and corresponds to the 

 fourth member above the base of the Puerco in the section previously 

 given along the Puerco River; this member was traced continuously 

 from the Nacimiento Mountains to beyond the Arroyo Torrejon. 



The sedimentary record as preserved in the strata of the Naci- 

 miento group is capable of slight variance of interpretation in respect 



Fig. 7. — Shale of the Nacimiento group, three miles northeast of Nacimiento, 

 New Mexico. Short distance west of the preceding view. 



to origin. It is evident, however, that they were deposited in fresh 

 water as shown by both the lithologic composition and the fossils. 

 The beds may be largely the result of accumulation of sediment on 

 the floor of an extensive fresh-water lake with alternate flooding and 

 withdrawal of water, or they may have resulted chiefly from confluent 

 alluvial fans along broad streams; or more probably the physiography 

 involved a combination of the two conditions. 



There is a notable absence of chemical deposits in the formations 



