146 NATURAL RESOURCES SURVEY 



the surface between the Cerrillos fields and the Divide and 

 so accounts for the abundant evidence of a continuation of 

 the coal fields from Cerrillos to Gallup. 



It seems practically certain that the area in question re- 

 presents in the times of the coal formation an old coastal 

 plain which extended entirely across the state and that this 

 old cretaceous coast line warped enough at times to vary the 

 conditions so as to make it favorable for the rapid and luxu- 

 riant growth of vegetation along this belt. As these warp- 

 ings increased in amplitude and frequency the conditions 

 favorable to coal deposits ceased and Carbonaceous shales, 

 characteristic of marshy conditions became prevalent these 

 are the formations which now outcrop so plentifully where 

 faulting is not a prominent feature in the geology. These 

 shales are well exposed along the cliff faces of Chaco Canon 

 twenty miles northwest of Seven Lakes. Since the period of 

 coal formation ceased along this east and west belt, there 

 have been notable changes in the topography. Enormous 

 erosion intervals as well as periods of deposition inter- 

 vened between the Coastal Plain period and the period 

 of vulcanism which covered not a small portion of the area 

 with a thick and protecting coat of lava. Then in turn came 

 a new order of affairs in which more faulting and erosion 

 brought things to their present state of complexity and ap- 

 parent incongruity. 



CLIMATIC HISTORY. 



Ever since the inauguration of dry land in New Mexico the 

 evidences are that semi-arid climate has been the rule. It 

 is true that the writer has found numerous examples of 

 petrification of Cretaceous vegetation but this can all be 

 accounted for without any vast change of climate. Several 

 authorities claim at least a humid Pleistocene climate. They 

 believe conditions which gave opportunity for heavy glacia- 

 tion to occur in the mountains of Colorado and throughout 

 the northern three fourths of the Cordilleran system, gave 

 an extremely humid climate to New Mexico, which is very 

 probable. It is undoubtedly the fact that glaciation and its 

 accompanying sources of water was responsible for many 

 lakes over the state, as for example, in the Estancia Valley. 



Arguing for these facts some may endeavor to bring these 



