1 88 Bulletin of Laboratories, of Denison University [v^oi, xi. 
laeviscula, E. Columbella, Liopistha concentrica, 'Comptonectes 
symmetricus, Baculites gracilis, Prionocylus woolgari. 
About ten feet of flags follow the dark shales, which are 
followed by about 75 to 100 feet of yellowish gray shales pass- 
ing upward into yellow sandstone about 75 feet thick. In the 
lower layers of sandstone or in the upper sandy part of the 
shale below it there are frequently developed large concretions 
often with a cement of iron. These concretions may be over 
four feet in diameter and often become conspicuous objects in 
the landscape. They have been found at so many places in 
the same place in the series that we have come to attach con- 
siderable importance to them as a means of identifying horizons. 
The concretions occur in the same relative place to the east of 
the Sandia mountains but there by reason of the great distor- 
• tion and metamorphim, have been distorted and flattened. Sev- 
eral species has been recovered from the concretions though 
they are not usually fossiliferous. At the top of this Tres Her- 
manos sandstone is a rather constant band of pinkish sandstone 
which preserves a uniform thickness and weathers separately 
from the underlying massive beds. When freshly broken this 
sandstone is saccharoidal and nearly pure white. Its greater 
consistency and convenient and uniform thickness may make it 
available for quarrying at some future time. 
Above the sandstone is a large series of very friable sandy 
shales which are everywhere so readily eroded as to leave their 
thickness somewhat obscure. They are broken by small layers 
of ferrugineous sandstone which are somewhat fossiliferous 
affording for the most part broken fragments. In the neighbor- 
hood of (sometimes above but oftener below) this series of sand- 
stone layers is a very widely distributed and conspicuous zone 
of concretions characterized by the abundance of calcite crystals 
and the occurrence of a plentiful fauna. These calcareous and 
septaria concretions often abound in large ammonite shells and 
large species of Pinna and Baculites which' weather out in a 
very good state of preservation. This zone has been found in 
the region of Cabezon mountain, south of the Nacimiento range 
and near Una de Gato east of the Sandia range always with 
