9 6 EDITORIAL 



who said too little. The correction of these evils should rest 

 with the presiding officers, but must originate with the Fellows 

 themselves. It is to be hoped that some regulations will be 

 formulated and put into operation at the next winter meeting in 

 Washington, D. C. 



J. P. I. 

 *** 



In an article on igneous intrusions in the October-November 

 number of this Journal, Professor Iddings states that, "Rus- 

 sell has called attention to what he considers volcanic plugs 

 in the region of the Black Hills of South Dakota." I desire 

 to deny the statement that the intrusions referred to were 

 called volcanic plugs ; abundant evidence was, I think, presented 

 to show that they are, as I termed them, plutonic plugs. They 

 are intrusions of igneous magmas forced upwards into hori- 

 zontally stratified rocks so as to raise domes above them ; but 

 did not reach the surface, and hence should not be considered as 

 occupying the conduits of volcanoes, and so far as can be judged, 

 did not expand laterally after the manner of laccoliths. Not 

 only one such intrusion was described, but several in various 

 stages of exposure by erosion, from an unbroken dome of strati- 

 fied beds, presumably with an intruded plug beneath, represented 

 by Little Sun Dance Hill, to the imposing fluted column of Mato 

 Tepee, over 600 feet high. Associated with these plug-like 

 intrusions are what appear to be true laccoliths, as Warren Peak, 

 for example. When this instructive region is more thoroughly 

 explored, we may expect to find a series of examples illustrating 

 the transition from plug-like to cistern-like intrusions or lacco- 

 liths. For these reasons it is well to hold the locality referred 

 to, as furnishing the type-group of plutonic plugs. 



The evidence just referred to was stated in the article 1 criti- 

 cised by Iddings, but without having seen the intrusions and 

 without presenting any new observations concerning them, he 

 brushes it aside and restates the same kind of evidence for the 



1 Igneous intrusions in the neighborhood of the Black Hills of Dakota, Jour. 

 Geol., Vol. IV, 1896, pp. 23-43. 



