VON BUCH ON THE LIMITS OF THE CHALK FORMATION. 23 



strata so peculiarly characterized by GrypTicea vesicularis, Belemnites 

 mucronatus and mamillaris, by Inoceramus Cuvieri and Cripsii, by 

 Ostrea Biluvii, Terebratula cornea and semiglobosa, by Ananchytes 

 ovata, Galerites vulgaris and albogalera, and similar fossils. Older 

 cretaceous strata first appear only in proportion as we descend to- 

 wards the south, and in the Caucasus, in Daghestan, these older 

 {neocomien) beds, according to the excellent observations of Abich, 

 attain a thickness of nearly 5000 feet. It resembles a mighty wave, 

 sweeping far down from the highest summits of the Caucasus and 

 gradually dying away on the margin of the older formations in the 

 plain [on the north] . 



Beyond the ocean the cretaceous formations terminate in the At- 

 lantic regions of the United States before they have reached the city 

 of New York, so that their limit scarcely touches the 40th degree of 

 latitude, or sixteen degrees lower than in Europe. In Kentucky and 

 Tenessee it remains below 37°. But it is very different far up on 

 the Missouri ; this great river flows uninterruptedly from the foot of 

 the Bocky Mountains for 1400 English miles, through strata of chalk, 

 at least as far as the mouth of the Sioux river. This is the result of 

 the accounts and collections of the Prince of Neuwied and of the re- 

 ports of the celebrated astronomer Nicollet. In these western parts 

 of America therefore, the chalk formation rises to 50° of latitude, or 

 full ten degrees higher than in the eastern portion. Here also it shows 

 a continuous extension greater than that of any other formation 

 known on the surface of the globe. Captain Fremont saw chalk strata, 

 fields covered with Inoceramus Cripsii, on the river Platte, Lieutenant 

 Abert on the Arkansas, and as far as Santa Fe in New Mexico, and Dr. 

 Wislicenus found them also beyond the Bio del Norte near Monterey 

 and Laredo, according to the reports published in 1848 by the Con- 

 gress in Washington. The Bocky Mountains and their continuation 

 to the east [west ?] of Santa Fe in New Mexico, have entirely cut off 

 this cretaceous sea. No trace of chalk was discovered either by Captain 

 Fremont on the Columbia river, or on the Humboldt river in the won- 

 derful ** Great Basin" down to the Pacific, or yet by the observantCap- 

 tains Cooke and Johnston in Sonora and California along the Bio Gila. 



Nevertheless the whole of this so vastly extended chalk formation 

 consists only of the upper beds. After very careful and accurate in- 

 vestigation, Sir C. Lyell decided, that in the whole of North America 

 chalk strata from the Maestricht beds down to the gault alone oc- 

 curred ; and Mr. Ferdinand Bomer, as the result of his highly valua- 

 ble and accurate researches in Texas, goes the length of considering 

 all the strata in that region, already so far removed from the Atlantic 

 coast, as entirely of the upper division, and not even once touching 

 on the gault. 



This peculiarity is, however, singularly enough limited to North 

 America alone. Even in Mexico deeper beds already appear to occur. 



M. Galeotti has brought Trigonise from Tehuacan, on the borders 

 of the province of Oaxaca, which he has described as Trigonia 

 plicatocostata * . This Trigonia belongs to the division of the Trigonice 

 * Bulletin de Bruxelles, iii. No. 10. 



