LOWER CRETACEOUS FORMATIONS AND FAUNAS 595 
or calcareous material, in bands only a few inches thick. There 
are also occasional thicker bands of sandstone, and sometimes 
' massive conglomerates. The larger bodies of shale frequently 
contain many calcareous concretions, and such concretions are 
sometimes found even in the coarse conglomerates. More rarely 
there are larger bodies of limestone, several feet in thickness, 
but they do not form continuous beds of any great extent. The 
conglomerates also appear to be local deposits of no great 
length, though sometimes of very considerable thickness.” The 
overlying Horsetown beds have essentially the same lithologic 
character and are distinguished mainly by marked differences in 
the fauna—especially by the absence of Aucella and the greater 
abundance and variety of the ammonites. Where the base of 
the Shasta has been observed it rests on metamorphic rocks of 
undetermined age. It is conformably overlain by the upper 
Cretaceous Chico formation which in its basal portion is proba- 
bly as old as the Cenomanian. 
The Lower Cretaceous has an enormous thickness at some 
localities on the Pacific coast. A sectionon Elder Creek, Tehama 
county, Cal., measured by Mr. Diller, showed about 20,000 
feet of Knoxville and 6000 feet of Horsetown beds without any 
evidence of duplication of strata. This thickness is exceptional, 
though other localities in the same region show apparent thick- 
messes of 12,000 to 15,000 feet: 
Although the Shasta group is of marine origin it has yielded 
a number of land plants from several different horizons ranging 
from the upper third of the Knoxville to near the top of the 
Horsetown beds. Professor Fontaine has recognized twenty-six 
different forms among them. He says that ‘all have their 
nearest relations in Lower Cretaceous forms, and there is no 
plant that would indicate an age different from Lower Creta- 
’ A large proportion of the species occur in the Potomac 
and a feware found in the Kootanie and in the Comanche series, 
none of which offers any other means of direct comparison with 
the Shasta. Here, as in the Kootanie, no dicotyledons have 
been found. 
ceous.’ 
