250 CHARLES KEYES 



the basal unconformity is coextensive with the one beneath the 

 Ratonan series on the opposite side of the Rockies, in which case 

 the Arculeta and Maya formations are homotaxial. The term 

 "Animas," which is sometimes appHed to the beds of the San Juan 

 basin is preoccupied. 



In the Nacimientan series are included the basal beds of the 

 old Wasatch group. It is regarded as earliest Eocene. It is sub- 

 divided into the Puerco clays and, the Torre j on marls and sand- 

 stones. The deposits are doubtless entirely epeirotic in character 

 and perhaps eolian. There is a large and varied vertebrate fauna. 

 The outcrop constituted one of Cope's favorite collecting grounds. 

 The beds have a maximum vertical measurement of 1,000 feet. 

 Marked erosional unconformities separate all of the Tertiary ter- 

 ranes of the San Juan basin. 



The Chaman series comprises the main body of clays, sands, and 

 shales of the San Juan Wasatch succession. Canyon Largo sand- 

 stone is Newberry's early designation. Chaco terrane covers the 

 principal clay deposits. Together they are nearly 2,000 feet thick. 



Of manifest later date are the Tertiaries of the Rio Grande 

 basin. These consist of the Galesteo sands and the Santa Fe 

 marls, 1,300 feet in thickness. Over the Llano Estacado the latest 

 Tertiary sands, 300 feet thick, are assigned to the Pecosian series. 



The terranal names applied to the New Mexican Tertiaries 

 cover only the main bodies of deposits. No doubt other titles will 

 eventually be attached to the numerous minor members. 



Quaternary deposits of New Mexico are chiefly desert con- 

 centrates. They are not mainly deflated materials, but accumu- 

 lations left behind after the main bulk of fine rock debris has been 

 sorted out and exported. The deflated dusts come to rest far 

 outside of the arid region. Gravel and bowlder trains are prin- 

 cipally the results of arroyo wash. Till-like materials are brought 

 down from the highlands. Some glacial till yet remains on the 

 sides of the highest mountains where ice fields were once feebly 

 represented. Adobe soil is deflated dust temporarily at rest. 

 Some fluviatile deposits are present. Lacustrine beds are rare, 

 very limited, and quite ephemeral. 



In the accompanying chart of New Mexican terranes the latter 

 are fitted to the Chamberlin and Sahsbury classification. 



