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SCIENCE. 



[Vol. IX., ^'o 224 



large groups, they give some broad indications of 

 a hiffhJy suggestive character ; and though affected 

 v.'ith great inequalities, which for the time being 

 seem to be anomalous, these anomalies are as in- 

 structive as the main facts themselves. 



We have given the preliminary plotting of the 

 intensities in the map before you. The first point 

 to which we shall invite attention is the magni- 

 tude of the area affected by the shocks. It was 

 sensibly felt in Boston, which is the most distant 

 point on the Atlantic coast from which affirmative 

 reports have been received. From Maine the an- 

 swers are all negative. Most of those from New 

 Hampshire are negative, but two or tliree positive 

 ones show clearly that it was felt in sensitive 

 spots. In Vermont, affirmative reports come from 

 St. Johnsbury and Burlington on LakeChamplain. 

 No positive reports come from the Province of 

 Quebec. In New York state it was felt in the 

 vicinity of Lske George, and at Lake Placid and 

 Blue Mountain Lake in the Adirondacks. In On- 

 tario it was quite noticeable in several localities, 

 though the great majority of reports from that 

 place are negative. In Michigan it was noted in 

 several places ; and at Manistee lighthouse, on 

 Lake Michigan, the trembling was strongly 

 marked. In Wisconsin, though many of the re- 

 ports are negative, it was felt quite strongly at 

 Milwaukee, and was also noticed at Green Bay 

 and at La Crosse on the Mississippi, 967 miles 

 from Charleston, — the remotest point within the 

 United States which has given a positive report. 

 In central Iowa and central Missouri it was un- 

 mistakably felt. In Arkansas the eastern portion 

 of the state from sixty to seventy-five miles west 

 of the Mississippi gives numerous positive reports. 

 In Louisiana the reports are mostly negative, but 

 numerous persons in New Orleans felt the shocks, 

 and recognized their nature. In Florida it was 

 universally felt, and in the northern part of the 

 state was severe and alarming. From the Ever- 

 glade region, of course, no reports have been re- 

 ceived, as it is uninhabited : but in some of the 

 Florida Keys it was felt in notable force. From 

 Cuba a few reports have come ; and the most dis- 

 tant point in that island which was shaken was 

 Sagua la Grande, where the vibration was very 

 decided. Lastly, a report comes from Bermuda, 

 a thousand miles distant from Charleston, which 

 leaves little doubt that the tremors were sensible 

 there. 



The area within which the motion was sufficient 

 to attract the attention of the unexpectant ob- 

 server would be somewhat more than circum- 

 scribed by a circle of a thousand miles radius ; and 

 the area of markedly sensible shaking, would, in- 

 cluding the oceanic area, be somewhere between 



two and one-half and three million square miles. 

 In this estimate, liowever, only well-defined 

 seismic movement of notable force is considered. 

 There are reasons for believing, that, by proper 

 instrumental observation, the movement could 

 have been detected over a much greater area. In 

 the first place, it is to be noted that the peripheral 

 portions of the observed area lie in districts which 

 are rather thinly populated, sometimes also in dis- 

 tricts which, from the nature of the ground, do 

 not disclose forcibly the passing shock. Further- 

 more, the passing wave in the outer portions of 

 the area was almost everywhere of an undulatory 

 character and of great wave-length, and, while 

 still retaining a large amount of energy, did not 

 often dissipate itself into those smaller and shorter 

 tremors which are very much more likely to at- 

 tract attention, though really possessing very 

 much less energy. Six hundred ■ miles from the 

 origin the long swaying motion was felt, and was 

 often sufficient to produce seasickness, yet was 

 unaccompanied by sound or by the tremulous 

 motion due to short waves. 



It will be observed upon the maj) that there are 

 several large tracts which show a comparatively 

 feeble intensity, while completely surrounding 

 them is the general area of greater intensity. The 

 most conspicuous of these areas of silence is the 

 Appalachian region. The facts here are extreme- 

 ly interesting and suggestive. It has been gener- 

 ally supposed that a mountain-range serves as a 

 barrier to the propagation of earthquakes, not 

 from any known relation of cause and effect, but 

 merely as the result of observation. In Japan it 

 is universal testimony that the central range of 

 the island marks the dividing-line between earth- 

 quake and no earthquake. The shocks, so fre- 

 quent there, are seldom noticed beyond the 

 mountains. A similar conclusion has been 

 drawn from South American earthquakes, and 

 also from those which have visited southern Italy. 

 As soon as the data in the earlier stages of the 

 inquiry began to indicate insulated areas of mini- 

 mum action, they were completely investigated, 

 and every effort has been made to secure full data 

 from them. The result has been to show satis- 

 factorily that such was the case. The Appalachian 

 belt south of middle Pennsylvania disclosed a 

 few spots where the. shaking was considerable ; 

 but in the main it was but lightly affected until 

 we reach the extreme southern portion of this 

 range, where the shocks begin to be somewhat 

 vigorous, even in the mountains. West and north- 

 west of the range, however, the force of the un- 

 dulations resumes even more than its normal vig- 

 or. In eastern Kentucky and south-eastern Ohio 

 the force of the shocks was very considerable 



