242 CHARLES KEYES 



discovered similar organic remains in the mountains lying to the 

 north of the same point. The section developed rapidly until it 

 reached a thickness of more than 500 feet, extended entirely across 

 the southern part of the state, and comprised three important 

 series corresponding to the three subdivisions of the period. 



These limestones are abundantly fossiliferous. The forms 

 indicate the same sub-periodic divisions that are commonly recog- 

 nized on the eastern side of the continent. Much of the bottom 

 and top of the general section for the continent is missing in New 

 Mexico. Between the Ordovician beds and the Cambrian below 

 and the Silurian above marked unconformities prevail so that the 

 first-mentioned unit is sharply defined. 



Silurian sediments are poorly developed. The rocks out-crop 

 in a thin broken line across the southwestern comer of the state. 

 That deposition during the period was extensive in this region is 

 quite manifest; but it is also evident that during Devonian and 

 Mississippian times the deposits were largely removed through 

 profound erosion. The contained fossils indicate only the Niagaran 

 horizons of the standard eastern section. 



From the character of the organic remains the presence of 

 Devonian rocks in New Mexico receives early announcement. 

 Both Antisell and Hall in 1856 call attention to the fossil evidence. 

 Dutton's statement that Devonian strata were generally wanting 

 in the eastern part of the Colorado High Plateau region is some- 

 what misleading. These rocks are really very much better repre- 

 sented in southwestern New Mexico than has been commonly 

 supposed. In the vicinity of Santa Rita, in Grant County, are 

 400 feet of light-colored, fine-grained limestones and shales which 

 carry abundant organic remains. 



Two parts of Devonian time appear to be represented. The 

 basal shales seem to belong to the mid-Devonian section; while 

 the limestones are late Devonian in age. A surprising feature is 

 that the fauna is the typical Lime Creek phase of northern Iowa. 

 This horizon corresponds to the uppermost part of the section 

 represented in the Upper Mississippi Valley, which is, according to 

 Tschernyschew, Williams, and others, who have given the subject 

 most attention, mid-Devonian in age. These authorities also 



