214 ~=B. F. Shumard on the Primordial Zone of Texas, 
these fossils illustrated with excellent figures. For one of the 
trilobites Roemer proposed the genus Prerocephalia, which appears 
to be nearly related, if not identical with Conocephalites of Zen- 
ker, another and unnamed species possesses all the characters of 
Dikelocephalus of Owen, while a third erroneously figured as 
the tail of the latter is evidently the head of a n Arionellus.* 
It is scarcely necessary to inform palebiciologiats that these 
ey are confined exclusively to the Primordial Zone, to which, 
indeed, Mr, Barrande has already referred the Texan strata, 
aioe” his ie ae upon the evidence afforded by the work of 
Reemer, last cited. 
We have no Oualiae account of the Primordial rocks of Texas 
until 1859, when the ee writer published a notice of their 
discovery in Burnet county (Trans. Acad. Sci., St. Louis, vol. i, p. 
673,) in which their parallelism with the Potsdam sandstone and 
Calciferous sand grou p of Iowa, Wisconsin and Minnesota and 
the ma eg limestone series (in part) of Missouri was indicated. 
Further explorations have shown that the Primordial rocks 
with their characteristic fauna are spread over considerable areas 
in the counties of Burnet, San Saba oe Llano, and that they 
also extend into McCulloch, Mason and Lampasas, and as cotm- 
cats little is known respecting their lithological and = 
tological features in this, i te 
The Primordial Zone of Texas may be described as a series of 
light colored, pure ghd impure dolomites, limestones, chert, cal- 
careous and silicious sandstones, gritstones and conglo omerate, 
presenting an aggregate thickness of from eight to ten hundre 
feet, and separable into two well marked divisions, of which the 
superior represents the Calciferous — group and the inferior 
the Potsdam sandstone of the northw 
These rocks are based on He feldspathic granite, very 
similar in lithological character and composition to the gra anite, 
which occurs in the region of the Iron Mountain of Missour%, 
and they are succeeded by even-bedded, hard, brittle, rg 3 
bly close-textured, pure limestone and alternating beds of very 
compact dolomite, sometimes elegantly variegate with delicate 
flesh-colored cloudin This formation, some of the beds 0: 
which resemble lithographic illo, has received the name 
of Burnet marble, and may possibly represent the Bird's-eye 
limestone of the New York series. The ossils hitherto discov- 
It affords me pleasure to acknowledge rig that in these ee Be I have 
ist oesaek te sentiat by Prof. W. P. Riddell of - tem Texas Ge Geuiegies} F ataer 
¢ Remer’s were found in the San Saba valley, M county. 
