306 D. W. JOHNSON VOLCANIC NECKS OF MT. TAYLOR REGION 



devoted to the lava-capped mesas and the buttes, however, give a good 

 idea of the essential features with which we are concerned, and offer the 

 best explanation 3et available as to the manner in which the great cylin- 

 drical masses of lava came up through the surrounding sediments. A 

 dozen illustrations show the typical appearance of the buttes. 



As seen in the field, the nature of the buttes is so evident that no one 

 who has seen them would doubt the manner of their origin. It is there- 

 fore not surprising that Duttou regards them as true volcanic necks and 

 does not discuss alternative theories or interpretations. We read on 

 page 167 that "the experienced geologist who has traveled much in these 

 regions will recognize their significance at a glance," and on page 168, 

 that "the interpretation here given is such as would be accepted at once 

 by any geologist, but the general reader might like some further proof 

 of it. He can have an abundance." Then follows a detailed description 

 of many of the buttes, which will be referred to again in subsequent 

 pages. 



Dutton was unable to visit the two finest buttes in the region, Cabezon 

 and Great neck, bvit saw them from a distance. My own observations 

 included these two and a number of intervening ones; so that the data 

 collected were not repetitions of those presented by Major Dutton, but 

 rather supplementary to them. 



Professor Newberry, in his report on the geology of tlie exploring ex- 

 pedition from Santa Fe to the junction of the Grand and Green rivers, 

 figures the great Cabezon ])C'ak on plate XI of the report, but does not 

 discuss its origin, except to say tliat it lias a general resemblance to the 

 ISToedles of the San Juan valley (page 117). Concerning the Needles ho 

 writes (page 107) : 



"This is a mass of erupted rock, rising with perpendicular sides from the 

 middle of the valley. ... Its altitude is about L700 feet above its base; 

 above the river, 2,202 feet. It is everywhere surrounded by stratified rocks, 

 and its isolated position and peculiar form render its origin a matter of some 

 little doubt. My conviction, however, is very decided that its remai-kable relief 

 is due to the washing away of the sediments which once surrounded it, and 

 which formed the mold in which it was cast. In no other way can I imagine 

 its vertical faces of 1,000 feet to have been formed." 



The figure of Cabezon, while not very accurate, shows the vertical 

 columnar structure, and the figure of the Needles (plate X) indicates 

 that the same structure is found in that apparent neck. 



Eeference has been made to tlie Devils tower, or Mato Tepee, of ^Yyom- 

 ing, and its interpretation as a remnant of a laccolith. Professor Jaggar, 

 in his paper, "Laccoliths of the Black Hills," mentions the occurrence of 



