CURRENT PRE-CAMBRIAN LITERATURE 527 
apparent thickness is 2400 feet, and this may be an overestimate, 
because the formation may be repeated by folding. The Thunderhead 
conglomerate consists of a series of conglomerates, graywackes, and 
sandstones, with many small beds of slate. ‘The thickness is believed 
to be about 3000 feet. ‘The Hazel slate is chiefly a black slate, but it 
contains many thin beds of sandstone and conglomerate in small 
quantity. ‘The exact thickness cannot be ascertained, but it is believed 
to be about 700 feet. The Clingman conglomerate is the same in 
composition as the Thunderhead conglomerate, except that in the 
Clingman conglomerate there is smaller development of slate beds. 
The age of the Ocoee rocks is undetermined, and they are there- 
fore mapped as of unknown age. 
Hayes* maps and describes the geology of the Cleveland quad- 
rangle of Tennessee. Ocoee rocks occupy the southeastern part of the 
quadrangle, forming Big Frog Mountain and the plateau along its 
western base. No fossils have yet been found in these rocks, and they 
are separated by a great fault from rocks of known age, so that their 
position in the stratigraphic column cannot be fixed with certainty, but 
since they bear the marks of extreme age, they are considered as 
probably Algonkian. ‘The Ocoee series comprises in this area the 
following formations, from the base upward: the Wilhite slate, the 
Citico conglomerate, the Pigeon slate, and the Thunderhead conglom- 
erate and slate. ‘Their correlation with formations bearing the same 
names in the Knoxville quadrangle to the northeast, described by 
Keith, is only approximate. The Wilhite slate consist in the main of 
dark blue or black slate. The Citico conglomerate varies from a 
coarse, massive conglomerate to fine grained sandstone or quartzite in 
sandy shale. ‘The thickness varies from 500 to 1150 or more feet. 
The Pigeon slate resembles the Wilhite slate, the chief difference being 
a frequently observed banding and an abundance of interbedded gray 
schistose sandstones and graywackes, and occasional conglomerates. 
The Thunderhead conglomerate and slate can be separated into three 
divisions. The lowest of these, from 800 to tooo feet thick, is a 
massively bedded conglomerate, made up largely of blue quartz and 
feldspar pebbles. The middle division consists of interbedded black 
slate and schistose conglomerate or sandstone, the slate apparently 
*Geol. Atlas of the U. S., Cleveland folio, No. 20, by C. W. Hayes: U.S. Geol. 
Sury., Washington, 1895. 
