OP ARTS AND SCIENCES. 



229 



IV. — The Taconic of Eureka (Nevada) and of the Grand 

 Canon of the Colorado River (Arizona). 



The important and unexpected discovery of the uppermost part of 

 the Potsdam at Saratoga with the same fauna as the Up[)er Potsdam 

 of Wisconsin, St. Croix River, Lake Pepin, and Trampaleau, is not 

 the only one that American stratigraphy owes to Mr. C. D. Walcott. 

 This savant,, whose studies on the manducatory and ambulatory ap- 

 pendages of the trilobites are justly celebrated, has in the last three 

 years, 1881, 1882, and 1883, made other discoveries of great value 

 in the regions of the Grand Canon, Arizona, and the Great Basin, 

 Nevada. Mr. Walcott gives the following general and ideal section 

 of the Taconic strata of the Grand Canon of the Colorado River. 



GENERAL AND IDEAL SECTION OF THE TACONIC ROCKS OF 

 THE GRAND CANON (COLORADO). 



Crystalline rocks. 



Note. — Plane of unconformity indicated by double dividing line. No trace of the Primordial 

 faunii, and of ttiu Supra-Primordial fauna, except in the ujpper part, or Saratoga and Wisconsia 

 subdivision. 



The npper part is formed of sandstone, shales, and limestone, 1,000 

 feet thick. Major J. W, Powell has called it the "Tonto Group." 

 Tonto means stupid; it is the name the Mexicans give to the Indians 

 of that region. The fossils are found in the middle and upper part of 

 the group, and belong to the genera Dikelocephalus, Crepicephahis, 

 Conocephalites, Jphidea, Lingulepis, and Cruziana. They indicate 

 the Upper Potsdam of Wisconsin, and of Saratoga County, New York. 

 The fauna of the Lower Potsdam of Keeseville, New York, and of 

 Highgate, Vermont, has not been found in the Grand Canon. 



