66 
GKOLOGY 
Stales and the shores of the northern Pacific Ocean. It forms the upper part of the high plains 
or table lands surrounding the Rocky mountains, and also of the famous Llano Estacado, the Tu- 
cumcari mountains, and los Esleros. Several extensive plateaux between Forts Bent, St Vrain, 
and Laramie, are partly formed by the Jurassic strata. It is also found near the village of Covero, 
near the Pueblo d’Acoma, on the western slope of the Sierra Madre, and near Fort Defiance. 
Since Grewingk’s discovery of the Jurassic rocks at Katmaiskoi', this formation has been pointed 
out in the vicinity of Sithka by Doroschin; on Vancouver’s island by Dr. Newberry; and finally in 
California by Dr. Trask. 
Cretaceous formation. This formation is, provisionally, divided in America into three groups; 
the first corresponding to the Neocomian, the second to the Green Sand and Marly Chalk.^ and the 
third to the White Chalk of Europe. The principal rocks composing it are : white yellowish lime- 
stone, green sandy clay, and white sandstone. Numerous fossils are found in each of the groups, 
the most characteristic are the following; Gryphega Pitcheri, Gr. sinuata var. Americana-, Exogyra fla- 
bellata; Ostrea carinata-, Caprotina Texana-, Toxaster Texanus-, [lolaster Comanchesi Pecten quinquecostalus ; 
Ammonites peruviunus. Am. Piedernalis, .Am. Shumardi , Am. nehrascensis ; Hamites Fremonti; Inoceramus Le- 
rouxi; Terebratula Harlani ; Belemnites mucronatus-, Ptychodus Whipplei , etc. 
Vannuxem first discovered the Cretaceous strata in New Jersey; they extend into Delaware, 
Virginia, both Carolinas, Georgia, Alabama, Mississippi, and Tennesse. This formation, bordering 
thus the Alleghany mountains on east and south , occupies a limited space at their foot , and is often 
covered by rocks deposited during the succeeding geological period. The alluvium of the Missis- 
sippi river does not allow the Cretaceous to appear in the valley of the river itself, but it is found 
again on the western side, in the southern part of the Stale of Arkansas, extending into Texas, 
where it forms a broad band reaching from Fort Washita and Preston to Laredo on the Rio Grande 
del Norte. The Cretaceous formation ascends the valley of the Rio Pecos , as far as Ilorsehead 
Crossing, also the Rio Colorado of Texas, nearly to its headwaters at the southern foot of the 
Llano Estacado, and it is found at the Elm Fork of Trinity river. 
North of Fort Washita, the Cretaceous is found only in isolated patches, the connection be- 
tween them having been destroyed by denudation. These isolated patches are found on both banks 
of the False Washita, on the Canadian river, at Little river, on the river Verdegris, the Arkansas 
near Fort Bent, the banks of the Republican Fork, the Blue river, and at Council Blulfs. Then 
they occur again along the right bank of the Missouri river, at Sage creek in the Bad Lands of 
Nebraska, and finally near Fort Union, Muscle Shell creek, and near the sources of the Missouri. 
The junction of Muscle Shell creek with the Missouri river is the most northern point at which 
the Cretaceous formation has been found as yet in America. 
In going up the valley of the Rio Grande del Norte, from Laredo to Santa Fe, the Cretaceous 
formation is found almost everywhere; it also forms the valley of the Rio Puercos near Albuquerque. 
It does not occur in the western slope of the Sierra Madre, and has not yet been noticed in the 
Pacific region i). 
I) 1 have learned since writing the above that Dr. J. Schiel, geologist of Capt. Gunnison’s e.xpe- 
dition, has found near Grand river, latitude 39°, longitude 109°, fossils that he thinks belong to the Cre- 
Mil 
