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referable to tlie Cretaceous. These benches occupy too considerable 

 areas, and are too uniform in their relations to one another (although 

 slightly undulating, as though deposited upon an uneven surface), to 

 admit of their present position being referred to the subsidence or set- 

 tling of portions of the same basaltic level. Yet they may have origi- 

 nated in one and the same outpouring of molten matter, which was 

 deposited upon or spread over the inequalities of the surface, preserv- 

 ing, as it were, the topographical features wrought at the close of the 

 Tertiary, and immediately preceding the epoch during which the pres- 

 ent contours were fashioned, and which latter involved alike the wasting 

 of the basaltic overflows and the old terrace-levels in the Tertiary and 

 Cretaceous, which were flooded by the igneous matter. 



Besides these less conspicuous deposits, there is the great basaltic 

 bed capping the Chicorica Mesa, in the midst of which there occur 

 what appear to be distinct volcanic cones and craters of later origin. 

 The Tauaja is probably an isolated remnant of the same great overflow, 

 which involved an immense extent of territory along the eastern flank 

 of the Spanish range, the actual extent of which may be inferred from 

 the wide distribution of the comparatively insignificant areas which 

 still exist in the mesas of Rayado and Gouzalitas, between the Cimar- 

 ron and Ocate, and probably other similar outliers farther to the south- 

 ward. As has been suggested by Dr. Hayden, the 'origin of these 

 immense outpourings of igneous products is probably due to immense 

 and innumerable fissures in the earth's crust, the direction of which 

 seems to have been determined by forces acting nearly at right angles to 

 the old axis of upheaval in the range to the west. Through these fis- 

 sures the molten matter escaped, overflowing extensive areas of the 

 Tertiary plateau and perhaps lower levels of the Cretaceous, as would 

 appear from the evidence afforded by the several distinct benches seen 

 to-day in which these basaltic deposits vary in relative level at least 

 1,500 feet, comparing the extremes, as represented by the lowest bench 

 on the borders of the Capulin Vega and the great bed forming the sum- 

 mit of the Chicorica Mesa, a few miles to the northwest. This great 

 outburst of basaltic-making materials probably antedates the formation 

 of the volcanic cones, which latter, it would appear, more properly per- 

 tain to a later time, or during the subsidence of the active period of 

 overflow, representing, as it were, the expiring throes of volcanic action, 

 where the forces were concentrated, and only manifesting their existence 

 in isolated centers of true volcanic crater-building phenomena. 



When we come to review the few facts elicited during a flying visit, 

 they seem merely to approach the threshold of a field the investigation , 

 of which would clear away all uncertainty respecting the origin and 

 relations existing between the various and diverse phenomena there 

 manifested. 



