610 TIMOTHY WILLIAM STANTON 
formations— the method in which each specific name is treated 
as a unit and the relative affinities of different deposits or local- 
ities are determined automatically by counting the number of 
common species. Here there are two great series of beds, each 
with a fairly large fauna, and not very far separated geographic- 
ally, and yet if directly compared they show no identical and 
very few related species. Again, these conditions are sugges- 
tive when considering a sudden complete change in successive 
faunas, such as is often seen. If the barrier between the 
Comanche and Shasta seas had been suddenly removed and the 
succeeding conditions had been favorable for the continuation 
of only one of the faunas, we would have had in one of the areas 
such a complete and sudden change in faunas in two successive 
beds that a long time interval might have been erroneously 
invoked to explain it. 
BIBLIOGRAPHY. 
I. PAPERS RELATING TO LOWER CRETACEOUS OF THE UNITED STATES. 
1823 Say, Thomas. Notes on fossils. Account of an expedition from Pitts- 
burg to the Rocky Mountains, by Maj. Stephen H. Long, Vol. II, pp. 
410, 411. Philadelphia. 
1834 Morton, S. G. Synopsis of the organic remains of the Cretaceous 
Group of the United States. Philadelphia. 
1840 Rogers, Henry D. Description of the geology of the state of New 
Jersey. Philadelphia. 
18417 Booth, J.C. Memoir of the Geological Survey of Delaware, including 
the application of the geological observations to agriculture, pp. 38- 
43. Dover. 
Rogers, W. B. Report of progress of Geological Survey of Virginia 
for 1840. Richmond. Reprinted in Geology of the Virginias, pp. 
437-449, 1884. 
1842 Rogers, W. B. Report of progress of Geological Survey of Virginia 
for 1841. Richmond. Reprinted in Geology of the Virginias, p. 
542, 1884. 
1846 Roemer, F. A sketch of the geology of Texas. Am. Jour. Sci., 2d 
ser., Vol. II, pp. 358-365. 
1848 Buch, L. von. Ueber Ceratiten. Abhandl. Akad. der Wissenschaften 
fiir 1848, pp. I-30, pls. 1-6. Berlin. 
