134 



are drawn on the basis of the intensities adopted in the Rossi- 

 Forell scale, they run about as indicated on the accompanying 

 map. It will be noticed that they center around one of the oldest 

 lines of disturbance in Illinois, the LaSalle anticline. The paral- 

 lel flexures in the lines on the west side are presumably due to 

 the northwest center. 



Two maxima were noted in the disturbance in the following 

 places: Bushnell, Canton, Qiampaign, Chicago, Geneva, and 

 Sterling in Illinois ; Davenport and Dubuque in Iowa. In Madi- 

 son, in Wisconsin, Professor W. H. Hobbs is reported having 

 noted three shocks. These may have originated in the three 

 epicentra noted. Observations on the duration of the distur- 

 bance sustain this evidence. Estimates on the duration of the 

 quake fall roughly into three groups, which average respecti- 

 vely four seconds (28 observations), thirteen seconds (12 ob- 

 servations), and sixty seconds (6 observations). It appears 

 likely that only one of the shocks was felt in the places where 

 *he duration was briefest, and that two shocks, or three, were 

 felt where the quake lasted more than ten seconds. All places 

 where the disturbance lasted for more than a minute are cen- 

 traly located and may have been affected by all three shocks. 



A classification of the senses involved in the observations 

 shows that the general sense of "well being" was concerned 

 in two instances. The sense of equilibrium was affected in 

 several cases in the mesoseismal area. Visible earthquake waves 

 are indicated for one of the epicentral tracts. Earthquake 

 sounds were heard by five observers. The shock was felt in 

 many instances. 



A classification of the terms used in describing the manner 

 in which various objects were affected by the disturbance is 

 shown in the table below, where the figures in parenthesis in- 

 dicate the number of times each term occurs in the reports. 



