62 SNAKE RIVER PLAINS OF IDAHO. [bull. 199. 
favors tne view that the lava came to the surface through fissures and 
was poured out after the manner termed by Richthofen fissure or 
massive eruptions, in distinction from the extrusion of molten rock, 
lapilli, etc., from well-defined vents, as in the case of Vesuvius and 
other well-known volcanoes. 
The A T iew that the lava forming so large a part of the Snake River 
Plains was supplied by fissure eruptions, interwoven with a graphic 
description of the leading scenic features of the region, is expressed 
in the following quotation from Sir Archibald Geikie's charming book, 
entitled Geological Sketches at Home and Abroad : a 
Never shall I forget an afternoon in the autumn of last year [1879] upon the great 
Snake River lava desert of Idaho. * * * We rode for hours by the side of that 
apparently boundless plain. Here and there a trachytic spur projected from the 
hills, succeeded now and then by a valley up which the black flood of lava would 
stretch away into the high ground. It was as if the great plain had been filled with 
molten rock which had kept its level and wound in and out along the bays and 
promontories of the mountain slopes as a sheet of water would have done, * * * 
I looked round in vain for any central cone from which this great sea of basalt could 
have flowed. It assuredly had not come from the adjacent mountains, which con- 
sisted of older and very different lavas, round the worn flanks of which the basalt 
had eddied. A few solitary cinder cones rose at wide intervals from the basalt plain, 
as piles of scoriae sometimes do from the vapor vents on the surface of a Vesuvian 
lava stream, and were as unequivocally of secondary origin. Riding hour after hour 
among these arid wastes, I became convinced that all volcanic phenomena are not 
to be explained by the ordinary conception of volcanoes, but that there is another 
and grander type of volcanic action where, instead of issuing from a local vent, 
whether or not along a line of fissure, and piling up a cone of lava and ashes around 
it, the molten rock has risen in many fissures, accompanied by the discharge of little 
or no fragmentary material, and has welled forth so as to flood the lower ground with 
successive horizontal sheets of basalt. Recent renewed examination of the basalt 
plateaux and associated dykes in the west of Scotland has assured me that the view 
of their origin and connection which first suggested itself to my mind on the lava 
plains of Idaho furnishes the true key to their history. 
The reference in the above quotation of " a few solitary cinder cones 
at wide intervals " is accompanied by a picture showing three conical 
mounds rising from a broad plain. This sketch is evidently intended 
to represent the three prominent elevations in the central part of the 
great plain to the northwest of Blackfoot, known as Big, Middle, and 
East buttes. As previously stated, these buttes were visited by me 
and found to be older than the Snake River lava, and entirely sur- 
rounded and separated one from another by it. Big and East buttes 
are the crumbling remnants of rhyolitic cones which rise as steptoes 
through the encircling basalt. Middle Butte is of stratified basaltic 
rock, and although its history was not definitely determined, it is cer- 
tainly not a cinder cone and does not mark a center from which the 
surrounding basalt came. The elimination of these three buttes from 
the list of cinder cones seems to make Geikie's conclusion as to the 
a New York, 1882, pp. 237-238, 242-245. 
