OF NORTH AMERICA 
41 
or Shiimard, and others are in such a bad state of preservation that I cannot describe them with 
any precision. I wish however to say a few words concerning some of the species described 
by my predecessors. That which is most wanting in the knowledge of the Cretaceous rocks of 
the United States, is the local study of details relating to the strata, and the exact stratigraphical 
position of each fossil. It is true that these rocks, being scattered over the country from the Up- 
per Missouri to the mouth of the Rio Grande del Norte, and the environs of Philadelphia, make 
such a study quite difficult, and also that the dangers presented by the Indian country of the North 
of Texas, the Upper Arkansas, New Mexico and Nebraska, place geologists far from the desirable 
condition of security required for making good surveys. Thus the greater part of the American 
Cretaceous fossils hitherto described were collected by persons having little or no geological know- 
ledge, and placed in the hands of paleontologists who had never seen the regions from whence 
they came. Morton had a profound knowledge of the Cretaceous strata of New Jersey; but he 
had not seen them in the South or West. Roemer has published good observations on the Cre- 
taceous rocks of the vicinity of New Braunfelds and Fredericksburg, Texas , but he gives no details, and 
his generalities are very vague. I have seen and studied the strata of the Upper Green Sand and 
the Marly Chalk at Timber creek and at Burlington, New Jersey; in the bed of Little river, one 
of the affluents of the Canadian; further I have recognized the Neocomian resting in discordant 
stratification on the New Red Sandstone on the left bank of the False Washita, near Comet creek; 
and finally I have found in the beds of white sandstone and gray marl of the environs of Albu- 
querque and Galisteo, New Mexico, fossils that have led me to consider these strata as the equi- 
valents of the White Chalk of Europe. But notwithstanding this practical knowledge, and my numerous 
researches in the Cretaceous rocks of Neuchatel, the Jura mountains, of Burgundy, the environs 
of Paris and the South of England , I confess I feel myself unable to classify with certainty all 
the Cretaceous strata found in the United States, and in my VII. Chapter, Terrain Cretace (See: 
Resume Explic. (Tune Carte Geol. des Etats—Vnis , etc. , in the Bulletin de la Soc. Gdol. de France. 2'""’' serie, 
tome XII , page 883.) , I divide them provisionally into three principal groups , taking care to pre- 
mise that as yet we possess no sufficiently exact study of details upon this formation. 
James Hall does not find the same difficulties and hesitations in his way, and without having 
studied practically the Cretaceous rocks either of America or Europe , he has classed them in a 
memoir entitled : Observations upon the Cretaceous strata of the United States , in the A'olume of Geology 
of the Report of the United States and Mexican Boundary Commission', Washington; 1856. It is true that 
the results arrived at are quite excentric , for he places in the Cretaceous period all the strata de- 
posited in the West during the New Red Sandstone and Jurassic epochs; and it is doubtless 
owing to this, that Henry D. Rogers has given so grandiose an extent to the Cretaceous rocks 
of the West in his Geological Map of the United States. 
EXOGYRA FLARELLATA Goldf. 
Observations. — Dr. F. Roemer gives beautiful figures and an excellent description ot this Texan 
oyster, that he calls Exogyra Texana. The figures are even too beautiful , of this and all the other 
Texan fossils given by the learned Professor of Breslau , and his desire to present perfect specimens 
has led him too far in restoring by combination, or even by induction, imperfect specimens, until the 
true condition of the fossil is no longer discernible. 
The Ex. Texana is very common in the Cretaceous rocks of Texas, and 1 have seen several hun- 
