ARTICLE XVI. 



Notice of the Oolitic Formation in America, rvith Descriptions of some of its Or^ 

 ganic Remains. By Isaac Lea. Read May 15, 1840. 



Baron Humboldt, in his " Geognostical Essay on the Superposition of 

 Rocks in both Hemispheres," mentions having met with the Jura Formation 

 (Oolite of Enghsh geologists) in Venezuela and other districts of Colombia, as 

 well as at Zacatecas, in Mexico; but I am not aware of any organic exuviae 

 having been described from this formation in the western hemisphere. 



Some years since, my friend. Dr. Gibbon, was appointed to attend a public 

 mission to Bogota, and, at my solicitation, kindly undertook to collect such 

 specimens in geology and zoology as he should think might interest me. 

 Among many other objects brought by him, I was very much surprised to 

 find several specimens of well characterized fossils of the Oolitic series, not 

 being then aware of any one having observed any part of that geological epoch 

 in our hemisphere. Other more pressing occupations have caused me to defer 

 the final examination of these interesting specimens until recently. On com- 

 parison with the fossils of the Oolite in my cabinet, from England, I find the 

 mass possessing the same mineralogical characters, being argillo-calcareous, 

 accompanied, occasionally, by sulphuret of iron, and the organic forms to be of 

 the same genera. The well known genus Trigonia presents several species, 

 one of which has a close resemblance to Trigonia clavellata, which, in Europe, 

 is distributed through many different beds of this group. The Ammonites, 



