PART 51 CHAZYAN AND RELATED BRACHIOPODS—COOPER v4 
Another quality of the correlations recorded herein must be stated to the 
reader so that he can better understand the difficulties involved. Correlations 
based on a single group of animals seldom if ever give the true story of relation- 
ships and correlation of strata. Correlation by complete faunas is the only sound 
method because different parts of a fauna may be retarded or advanced and 
only the sum total gives the truth. The present chart is based mostly on evi- 
dence deduced from a study of brachiopods, and most of the relationships herein 
depicted were detected by comparison of brachiopod faunules. However, when 
Dr. B. N. Cooper was making his studies of the trilobites of these same rocks at 
the National Museum in 1946, we were in close touch. Correlation by trilobites 
closely parallels that based on the brachiopods. A careful check by bryozoans, 
which are very numerous in the Appalachians and elsewhere, is a natural sequel 
to the present studies. 
In preparing the chart I did not completely overlook the value of other fossils, 
but, on the other hand, I was well aware of the unreliability of some “guide fos- 
sils.” Reference is made to Cryptophragmus antiquatus, Tetradium cellulosum, 
and Maclurites “magnus.” Cryptophragmus is now known to have a long range 
and thus not to be an absolute indication of the Lowville or Pamelia as hitherto 
believed. JT. cellulosum is known from Trenton rocks as well as Lowville. 
Maclurites is long-ranged and is not an infallible guide to the Chazy, as con- 
fusion in Pennsylvania between Lemont and Hostler shows. 
The chart contains five new stage terms which are designed to divide this part 
of the Ordovician into related parts. These stage terms are here proposed by 
myself and B. N. Cooper. Older stage terms, such as Chazyan and Black River, 
are no longer of use because these have been so defined that they do not describe 
the stratigraphy, or, as in the case of the Black River, the interval represents 
only a part of what we regard as a natural grouping of faunas. Grabau’s (1909) 
usage of Chazyan included the Black River, which we regard as more closely 
related to the overlying Rockland than to the Chazy group below. The Ulrich 
(1911) conception of the Chazyan was for the interval between the Lowyville 
and the top of the Canadian (Beekmantown or Knox dolomite), which is far 
too inclusive. The name Bolarian (Kay, 1948, p. 1402) includes two divisions ; 
Hatterian and Hunterian, but these, too, are unsatisfactory to show the relation- 
ships as B. N. Cooper and I understand them. The Hatter formation, whose time 
designation is Hatterian, appears to be the same as Hunterian if, as shown in this 
monograph, the Hatter is equivalent to Ridley. The Hunterian includes Low- 
ville, Chaumont, and their equivalents, but besides them Kay adds the Witten 
formation. The Witten, with its Pionodema and Doleroides, is placed by B. N. 
Cooper and myself as a correlative of the Rockland. Furthermore, the Rockland 
fauna is closely tied to that of the Chaumont, as I understand those fossils. Thus 
Bolarian is unsuited to depict the stratigraphic situation as understood herein. 
It was not a simple task to find satisfactory names for the stage terms here 
offered, but the sequences named are well exposed in the vicinity of the geo- 
graphic locale selected. 
Whiterock stage.—This name is taken from Whiterock Canyon in the Monitor 
