Grove Karl Gilbert 



6i 



Dr. Gilbert was the first to announce the fact that many fire- 

 rocks had ascended from hearths or centers beneath the earth's 

 surface and had forced themselves between sheets of rocks 

 separated by a zone of relative weakness. As the rock-sheets 

 were forced apart differentially by the ascending column of 

 molten rock, the latter occupied the space so formed and took 

 on the form of huge lenses, to which Gilbert gave the name of 

 laccolites, or laccoliths, meaning lake rocks. These he saw first 

 in the Henry Mountains. Gilbert became famous in England 

 by reason of this discovery ; but to the writer he confided the 

 belief that EngUshmen praised him for very little, inasmuch as 

 ''the laccolite was there," said he, "for the seeing." He it was, 

 also, who appreciated first the fact that areas such as the high 

 Wasatch Plateau, or Range, near Provo, and the relatively low 

 plain around Salt Lake, had formed a continuous surface at 

 one time, but were now broken or "faulted" blocks, one por- 

 tion of the plateau or plain sinking and the other rising, or both 

 rising, but one to a greater altitude than the other. This enor- 

 mous "Wasatch Fault" he actually understood from a mere 

 glimpse out of a window of the transcontinental train. This 

 led to his principle of the physiographical criteria of faulting. 

 Later on he was enabled to prove the fault origin of the plateau 

 from physiographical considerations. 



As with the laccolite theory, so also with the idea of the 

 "Physiographic Fault" ; Gilbert thought it was an easy thing to 

 understand. To which the writer responded : "It is a strange 

 thing that, of all the geologists who had seen the laccolites, and 

 who had traveled in the transcontinental trains, no one had un- 

 derstood these things until Gilbert announced them!" It is 

 also true that years afterward Gilbert had difficulty in making 

 European geologists see these "faults," even when he had 

 shown them the criteria of faulting on the spot. At the pres- 

 ent time, however, his work on faults of this type is universally 

 accepted by scientists of eminence. 



A great principle enunciated by Gilbert in 1882-1888 was 

 that concerning the action of streams and waves. He showed 

 that streams and waves accomplish most of their cutting or 

 erosive work during violent floods or storms. This point had 

 not been understood before, although certain great hydraulic en- 



