240 
FRAMEWORK OF ARIZONA 
of limestones, representing Early and Late Ordovicic times, are 
present. They are known, in the Clifton District, as the Longfel¬ 
low limestones, and the Armedaris limestones that extend west¬ 
ward from New Mexico. The two rock series are separated from 
each other by a notable unconformity, which may stand for all Mid 
Ordovicic time; and at the top and the bottom by like sedimental 
breaks from other formations. 
Over the boundary to the east, in New Mexico, the Longfellow 
limestones and associated beds of Late Ordovicic age form the 
Mimbresian Series. This is not the Mimbres limestone of later 
usage in the Government reports, which really comprises a curious 
medley of undifferentiated strata that are now known to cover 
sediments of several geological ages, Siluric, Ordovicic, Cam¬ 
bric and possibly others. 
Rocks of Siluric age seem not to be generally recognized in 
Arizona State. None of the numerous Government reports make 
mention of them. This is all the stranger since many good expo¬ 
sures carrying abundant characteristic fossils occur not only in 
this state, but just over the line, in New Mexico, where they are 
reported for more than half a century. More than twenty years 
ago, also, Reagan collected many of the most typical Siluric forms 
of organic remains from limestones northeast of Globe, in the Salt 
River valley; and he there measured 70 feet of cherty limestones 
which yielded these species. 
The several members of the Siluric section, as differentiated and 
named in New Mexico recently, seem to persist without notable 
change into eastern Arizona. Westward from the boundary the 
sequence rapidly becomes attenuated and fails altogether long be¬ 
fore the Grand Canyon is reached. Possibly layers of Siluric age 
are represented in the upper part of the Longfellow limestones in 
the Clifton District, and also of the Mescal limestones of the Globe 
District. 
Notwithstanding the fact that it was severely limited in its orig¬ 
inal deposition and by subsequent erosion before Carbonic times 
set in, the Devonic terranes of Arizona are among the most impor¬ 
tant stratigraphic units. They extend unbrokenly entirely across 
the state from the southeast corner to the northwest corner. Only 
Late Devonic time appears to be represented by these sediments. 
They recline on a peneplanation surface that was as long in form- 
