132 



basins entirely submerged, so that the cephalopods and corals 

 of the northern province were permitted to spread into this 

 southern sea embayment, and the general Onondaga fauna 

 was able to migrate freely from north to south across the east- 

 ern interior portion of the continent. 



J. A. Udden presented a paper of which the following is an 

 abstract. 



OBSERVATIONS ON THE EARTHQUAKE IN THE 

 UPPER MISSISSIPPI VALLEY, MAY 26, 1909. 



Earthquakes are infrequent in this region, and notes on 

 our seismic phenomena are the more desirable. This com- 

 munication is based mostly on items gathered from forty 

 weekly and ten daily newspapers published in the disturbed 

 area, and includes observations made in more than one hund- 

 red different localities. These data are given below, referred 

 to the several localities.* 



The area sensibly disturbed by this earthquake extended over 

 the greater part of Illinois, Iowa, Wisconsin, Michigan, Indi- 

 ana, Missouri, and Minnesota, a region about eight 

 hundred miles in diameter. The mesoseismal area appears to 

 have been triangular in form and unusually large, the greatest 

 violence having been noted near Plattcville, in Wisconsin, and 

 in Waukean and Bloomington, in Illinois, which places prob- 

 ably were separate epicenters. The velocity of the earthquake 

 waves, calculated from the reported observations on time re- 

 corded by government observers in Peoria (8:38 A. M.) and 

 in Washington, D. C. (8:41 A. M.), is 3.3 mile per second. 

 While no great reliance can be placed on these figures, as the 

 data are too few and their authenticity uninvestigated, yet the 

 great size of the mesoseismal area is in harmony wih the velocity 

 of the wave. Both indicate a great depth of focus. The highest 

 seismic intensity was above seven of the Rossi-Forell scale. 



The facts presented in the reports are sufficiently full to in- 

 dicate approximately the position of the isoseismals. When these 



