Correspondence. 289 
and eastern New York, which appear to be permeated with Hamilton 
fossils, arc not of the age of the Hamilton group, but represent a later 
geological stage, and that the fossils have, in a considerable degree, un- 
dergone modifications from their typical expression in the true Hamil- 
ton fauna. As the quality of these variations is hardly palpable under 
ordinary circumstances and has not been satisfactorily expressed in 
words, it ought to appear in composites based upon sufficient data: and 
should there prove to be differences in the fundfimenta of specific varia- 
tions, from the true Hamilton fauna, and of those from the alleged but 
contested Hamilton fauna above, the argument from such evidence 
would be entitled to serious consideration. J. M. Clarke. 
Albany, A. Y.. Feb. .'..'. 1894. 
"The Columbian Exposition; Notes on some Mesozoic and Terti- 
ary Exhibits. " An editorial under the above heading in the March 
number of the Geologist, which, though unsigned, was evidently writ- 
leu by Prof. F. W. Cragin, includes notes on several species of Creta- 
ceous fossils exhibited by the U. S. Geological Survey. As these notes 
contain a number of queries, either expressed or implied, I beg space in 
which to answer them seriatim, though several of them will lie more 
fully answered in a forthcoming bulletin (No. loii) of the Geological 
Survey. 
In explanation of the fact pointed out by Prof. Cragin that the labels 
in several instances did not agree with the nomenclature and opinions in 
his "Contribution to the Invertebrate Palaeontology of the Texas Creta- 
ceous," it isonly necessary to remind the reader that the collection was 
on exhibition in Chicago for some weeks before the book was published. 
The "two very interesting specimens of Gryphaea, labeled '•JSxogyra 
suborbiculata Lamarck,''" really belong to Exogyra, as that artificial but 
convenient genus is denned. Unfortunately the specimens exhibited do 
not show very clearly on casual inspection the distinctly spiral beaks of 
both valves. 
The occurrence of Radiolites austinensis in tin' Eagle Ford shales ought 
not to be considered remarkable when it is known that there is no dis 
Unci fauna! break between that formation and the Austin limestone, in 
vvhi(d) it is well known to occur. 
Comparison of thetypesof Trapezium micronemum Meek. Barbatia coal- 
nllenszs White (both from Coalville. Utah), and other specimens from 
Utah, together with the Texan fossils that Prof. Cragin has since de- 
scribed as Area galliennei d 'Orb. var. tramitensis, convinced me that thej 
all belong to one species, and they were placed under the earliest Ameri- 
can specific name as Barbatia micronema. It is evidently closely related 
to the European species to which Prof. Cragin refers it. but whether 
they are reall.v identical can hardly be decided without direct compari- 
son of specimens from both countries. In Utah Barbatia micronema oc- 
curs with Glauconia coalvillensis, Ostrea soleniscus, etc., in beds slightlj 
below the horizon of Buchiceras swallovi and probablj verj near the 
horizon of l he Texas Timber ( 'reek beds. The strata containing them 
in Utjah are intimately connected both faunallj and stratigraphicallj 
