PROCEEDINGS OF THE POLYTECHNIC ASSOCIATION. 475 



down into Mexico, and, according to Humboldt, even into Guati- 

 mala. These have all been extinct for many years. Scoria and 

 pumice stone have been found floating down the Missouri river, 

 supposed to have come from some volcano still in action. 



Dr. Vanderweyde. — Pumice stone is found floating down the 

 Khine, supposed to have come from extinct volcanos. 



Dr. Stevens. — The pumice upon the Missouri is of fresh appear- 

 ance, as if recently from the fire. 



While the tertiary rocks, lying between the Sierra Nevada and 

 the coast range were consolidating, Mount Diabolo, and Mount 

 Shasti Avere elevated. That system extended up into the Russian 

 possessions. But for this ancient outflow of volcanic matter, we 

 could now build, at a slight expense, a railroad running up 

 through this valley, turning around the Sierra Nevada, passing 

 the liumboldt mountains, going through the great gap in the 

 Eocky mountains, and so on to St. Louis, across to Chicago, by 

 Little Falls to New York ; and, excepting at Little Falls, we 

 should not encounter a mountain upon the whole route ; gradu- 

 ally rising six thousand feet above the level of the sea, and then 

 slowly descending to the Atlantic coast. Subsequent to this age 

 volcanic mountains were thrown up in the valley of Utah ; and 

 there we have the only burning volcanoes in the United States. 

 They exist there as large lakes, and are exceedingly interesting 

 and curious to travellers. 



Scientific men have devised two theories to explain the pheno- 

 mena of earthquakes ; one that they are caused by a collapse of 

 the earth's crust upon the liquid mass beneath, and a consequent 

 surging backwards and forwards of the great molten sea beneath 

 us. I do not understand how that could produce such an 

 instantaneous movement of the earth over such a great extent 

 of country. The earthquake wave seems to travel with a speed 

 almost equal to that of lightning. I consider the true cause of 

 earthquakes as yet undeveloped by scientific research. 



SUCTION DREDGING. 



Mr. Fisher suggested that the apparatus for dredging by 

 pumping, explained by Mr, Johnson, would be useful also for crea- 

 ting an artificial obstruction or bar for the purposes of blockade. 



Dr. Stevens stated that there are no boulders south of this 

 port ; that on the Jersey shore the largest pebbles are no larger 

 than a hen's egg, growing smaller as we proceed southward, the 

 principal substance being sand. 



