128 Association of American Geologists and Naturalists. 



The most important phenomena of volcanoes were discussed with a 

 view to determine the mode of formation of volcanic mountains. Sev- 

 eral illustrations and models were presented to exhibit these phenomena. 

 Volcanoes were shown to have that regular dome-like form which would 

 seem to belong only to masses uplifted and formed by a single effort. 

 It was shown that their internal structure is wholly unlike that of the 

 superficial beds which form their lower slopes, and is that of masses 

 originally formed in a horizontal position. Repeated instances were 

 cited of the formation of mountain masses by elevation at the first out- 

 break of the volcanic power, and it was inferred that all recent erup- 

 tions sensibly uplift the mountain pile. 



The mode of formation and the distribution of lava streams, and the 

 eruption and mode of distributing the ejected incoherent materials, were 

 described. It was shown that lava streams of recent eruptions are nev- 

 er arrested in large beds on the higher parts of the volcanoes, and con- 

 sequently do little to increase the mountain in height. The incoherent 

 materials do little more, but are carried by torrents and inundations to 

 the lower slopes of the volcano. 



From the consideration of all these facts, the conclusion was drawn, 

 that all volcanic mountains are formed by the paroxysmal elevation of 

 their rocky strata from below, and that modern ejections act only to in- 

 crease their extent and to level their bases with the surrounding plains. 



Dr. Henry King proposed to give a sketch of the geology of 

 the Valley of the Mississippi, from the southern part of the State 

 of Missouri to Wisconsin River, in the Territory of Iowa. 



The limited time he had allowed himself, from a knowledge he had 

 of other business which must come before the Association, would neces- 

 sarily oblige him to do great injustice to the subject, by causing him to 

 leave out a great many important and even necessary details. 



He called the attention of the Association to the primary formation 

 in the southern part of the state of Missouri, consisting of syenite, por- 

 phyry, and other igneous rocks, rising into low ridges, with a direction 

 nearly north and south. A kw miles south of this part of the state 

 was the earthquake region, rendered memorable by the earthquakes of 

 1811-12, that nearly destroyed the town of New Madrid, on the Mis- 

 sissippi river, and where ever since shocks of earthquakes have been 

 felt at very limited intervals. On these igneous rocks an upheaved stra- 

 tified deposit of a very ancient character, probably gneissoid, appeared 

 to rest. But Dr. King had not an opportunity of examining them suffi- 

 ciently in detail to arrive at any very satisfactory conclusion in relation 

 to their character. 



From this point in Missouri to Wisconsin River, a section presents the 

 evidences of one undisturbed, continuous, regular basin, with all the 



