aE\VETT] RIO GRANDE VALLEY, NEW MEXICO 21 



It is also evident from the investigations that eruptive activity has occurred in 

 the Texas-New Mexican region from Cretaceous to the present time, and at least three 

 well-defined epochs are at present recognizable which may serve as a guide to future 

 observations, viz: 



1. The Austin-Del Rio system, or Schumard knobs; ancient volcanic necks or 

 laccolites bordering the Rio Grande embayment, begun in later Cretaceous time, the 

 lava sheets of which have been obliterated by erosion. 



2. The lava flows of tlie Raton system, which are fissure eruptions of Tertiary time, 

 and which are only partially removed by erosion. 



3. The cinder cones and lava flows of the Capulin system, which are late Pleistocene, 

 and which still maintain their original slope and extent. 



This question was made the subject of investigation by tlie late 

 Prof. ('. L. Herrick, wliose geok)gical interpretations, it need hardly 

 be said, command high respect. He says: ' 



Much time has been expended in the effort to determine the precise age of these 

 basalt sheets and the results seem to be unambiguous. The fact that these lavas flow 

 over the bases of the trachyte and rhyolite mountains and flows, as at Soeorro, and burst 

 through and are interbedded in the tufa sheets as at Cochiti district, shows the basalt 

 period to follow the trachyte period of eruptive activity. Direct superposition on 

 the Tertiary sands in numerous places indicates their Post-tertiary age. Often the 

 Tertiary strata are much altered and reddened by the contact, being baked and 

 indurated in those places where the flow was thickest but less altered by the thinner 

 portions of the sheets. The question as to the period that may have elapsed since 

 these flows is more difficult of solution. We have so far failed t o find an instance where 

 the lava has flowed over the river deposits of supposed Pleistocene age. . . . It 

 has been repeatedly stated that these lavas are of recent date and that they cover 

 remains of human industry. So far as this portion of the territ'ory is concerned this 

 may l)e emphatically denied. Specimens of maize embedded in what was presumed 

 to be lava have been displayed in proof of the statement that man existed prior to these 

 lavas. It is not denied that recent igneous flows have occurred in various parts of the 

 West, but it seems very improbable that even the latest of these basalts could have 

 been cotemporaneous with man in New Mexico. An analysis made by Mr. D. W. 

 Johnson of the so-called lava containing corn proved it to be highly acid and to have a 

 composition impossible for basalt or an ordinary slag. 



There have come into the hands of the writer specimens of charred 

 corn imbedded in so-called "lava" from four sites in the Rio Grande 

 drainage and one ui the San Juan. Two of these specimens came 

 ])robably from the sites examined by Doctor TIerrick, namely, the 

 Jemez valley below Jemez pueblo and the Canada de Cochiti. The 

 writer's examination of these confirms his results. Analysis of one 

 specimen obtained from the vSanta Fe valley and of another from the 

 Chama valley disclosed the fact that the material bears no chemical 

 relation to basalt, being an acid product often resulting accidentally 

 by the action of fu-e on ordinary adobe soil. The specimens present 

 superficially the appearance of true lava. 



There is as yet no evidence that there was human occupancy ante- 

 rior to or contemporaneous with the New Mexico lava flows, thougli 

 these are, geologically speaking, of recent occurrence, possibly not 



' In Bulletin of the Scientific Laboratories of Denison University, xi, p. 180. 



