26 
LACCOLITHIC MOUNTAINS 
oir in which the term laccolith was first defined Maclaren ^ 
described as typical and as perfect laccolithic mountains as any 
later writer pictures forth. Other Scotch geologists long ago also 
directed attention to similar structures. 
Nor was this country very far behind in recognizing this class 
of mountains. Long prior to the appearance of the sumptuous 
monograph on the Henry Mountains typical laccolithic phenomena 
were, within plain view of that group, clearly pointed out and 
fully described. Very much in the same manner as subsequently 
discussed by the author of the monograph similar forms of lacco¬ 
liths were outlined and their essential characteristics and structures 
faithfully portrayed. Previous to Gilbert’s entering the southern 
Utah field his identical explanations of laccolithic origin of cer¬ 
tain Great Basin mountains was succinctly set forth and repeated¬ 
ly offered. Under the title of “Eruptive Mountains” was this 
particular orograpic type widely known to many of his predeces¬ 
sors and contemporaries in the region. 
In the Utah country, J. S. Newberry, geologist to the Macomb . 
expedition, appears to heve been the first investigator to call at¬ 
tention to that especial type of orographic structure which years 
afterwards came to be designated the laccolithic mountain. So 
early as 1859 Newberry,^ after visiting the Sierra Abajo, situ¬ 
ated 100 miles east of the Henry Mountains, in eastern Utah, 
accounted for its peculiar structure by regarding it as an eruptive 
nucleus on which steeply reclined the sedimentaries. He also spent 
several days on the Sierra La Sal, forty miles to the north, to 
which was ascribed a similar origin. His descriptions leave no 
doubts concerning the laccolithic nature of both mountain groups. 
Various members of the U. S. Geographical and Geological 
Surveys of the Territories, clearly describe laccolithic mountains. 
A. R. Marvine’s lucid descriptions^ of the Elk group of laccoliths, 
in western Colorado, are particularly noteworthy. To this sin¬ 
gular orographic type F. V. Hayden early applied ® the title of 
“Eruptive Mountains.” W. H. Holmes’ sketches® of the Elk 
Mountains display clearly the wedge-shaped masses intrusive in 
2 Geology of Fife and Gothians, p. 100, 1839. 
3 Geology of Macomb Kxped., p. 100, 1876. 
4 Seventh Ann. Rept. U. S. Geog. and Geol. Surv. Terr., for 1873, p. 186, 1874. 
5 Ibid., Eighth Ainn. Kept., for 1874, p. 55, 1876. 
6 Ibid., Eighth Ann. Kept., for 1874, pp. 62-64. 
