OF NORTH AMERICA. 
19 
seen to the North, in the direction of the Canadian river, and between the Canadian and the Ra- 
ton Mountains, as well as the majority of the mesas, which extend from the Rio Pecos to the foot 
of the Sierra de Sandia. Our survey has also met with it on the other side of the Rio Puerco, 
forming with volcanic lava almost the whole road between Covero and the Sierra Madre, and li- 
in Normandy. When I had found them in the strata itself and had collected a hundred in perfect pre- 
servation, I no longer doubted their identity with the Gryphwa dilatala (Plate IV. , fig. 1 . , 1 a, 1 b , 2. and 3.) 
of the Oxfordian group of England and France. Soon after, in the same zone with the Gryphwa, I found 
two specimens of a valve of Ostrea Marshii (Plate lY., fig. 4.) a very characteristic fossil of the Lower 
Oolite of England, France and Germany. This discovery of Jurassic fossils proved to me that I had at 
last met with the true Jurassic rocks in North America. 
To return to Pyramid Mount. — Above the fossiliferous JSlue clay are beds of a sandy limestone (F.) 
of a deep yellow color, and very hard; when broken it shines and shows brilliant points, like the vel- 
low limestone of the Inferior Oolite of the Jura. These beds ai'e each five or six feet thick and rise 
to the top of the Pyramid, where the upper strata is a white siliceous and very compact fimeslnne (G.) , 
resembling lithologically the Forest Marble ( Calcaires de la Citadelle ) of the environs of Safins and Be- 
sanQon. 
1 have no doubt that a minute survey, and a month’s stay in the vicinity of Plaza Larga and Tii- 
cumcari, would give more ample evidence of my^ determination of the Jurassic formation, by bringing to 
light more species of fossil remains. But as it is, my discoveries show' clearly that this formation is 
older than the Cretaceous — I have since found the Cretaceous rocks lying upon the Jurassic formation in 
discordance of stratification at Galisteo near Santa Fe, New Mexico — and more recent than the strata 
of the Keuper or New Red Sandstone vihich underlies it. Besides, the fossils that 1 found at Pyramid Mount 
when submitted to d’Archiac, de Verneuil, Deshayes, Elie de Beaumont, Dufrenoy, Agassiz, Barrande, Lyell , 
Murchison, d’Orbigny, Pictet, Oppel , Merian , Thurmann, Studer , Escher de la Linth , etc., were identified 
with the Gryphwa dilatata Sow', and Ostrea Marshii Sow. of England, France, Switzerland, Germanv and 
East Indies. The natural consequence is, evidently, that this formation of the Llano Estacado, Tiicutn- 
cari and Pyramid Mount, is equivalent to the Jurassic rocks of Europe and Asia; and that it represents 
in North America, the well known rocks of my native mountains, the Jura. 
Until that discovery' the existence of the Jurassic formation in both Americas was quite problematic , 
and the great Leopold de Buch, in his last memoir published a few' days before his death, denies the 
existence of the Jurassic rocks in South and North America; except in Russian America , w'here Grewingk 
has found it at the peninsula of Aliaska, in the bay' ofKatniai, Katmaiskoi village; but, as de Buch re- 
marks, that part of Russian America is more Asiatic than American. However I think de Buch has gone 
too far in his criticism of the fossils discovered by Domeyko and Darwin in Chili, and described by Ed. 
Forbes, d’Orbigny, Bayle and Coquand; and to Domeyko is due the honor of having first discovered the 
Jurassic Rocks in the New World. 
The Jurassic Rocks do not exist on the Atlantic slope of North America, nor anywhere Fast of the Mis- 
sissippi river ; they are first found at 102° of longitude west from Greenwich, and are confined to the 
most central part of the continent, bordering the Rocky Mountains which they form in part. 1 suspect 
that they w'ill not be found in Old Mexico, except perhaps in the northern parts of the States of Chi- 
huahua and Cohahuila ; but they extend towards the sources of the Missouri river , and along the Mac- 
kensie river; covering probably a large space of the North-Western territory of the Hudson bav Com- 
pany, of the Russian American territory (Doroschin, Mining Engineer, has found Jurassic fossils in the 
vicinity of Sitkha and other Russian localities.), and of the numerous Islands signalized by Mac-Clure, Parry, 
Belcher (Vertebra* and ribs of a Jurassic Ichthyosaurus discovered at Exmouth Lsland. ), in the North 
Polar Sea. 
