MICHIGAN ACADEMY OF SCIENCE. 51 



map of the Atlantic coast states. The more prominent Uneaments are here 

 brought out in dotted Hues, and it will be noted that upon them are ranged 

 the spots which indicate earthquake damage in the past and presumable 

 earthquake danger in the future, with the largest of the spots at lineament 

 intersection. Note, for example, the "northern fall line/' on which are 

 ranged Washington, Baltimore, Wilmington, Philadelphia, Trenton, New- 

 York, New Haven, East Haddam (Conn.), and Boston. This line marks a 

 well known fracture in the earth's crust at which formations of widely differ- 

 ent geological age have been joined and where slight falls in rivers have de- 

 termined the head of navigation, and with it the location of the port cities. 



The largest spot upon the map is East Haddam, Connecticut, where the fall 

 line intersects the straight gorge of the lower Connecticut. From the earliest 

 colonial days this town has been shaken by light earthquakes which have 

 generally not affected the surrounding country and which have been accom- 

 panied by subterranean rumblings. Upon its site stood the ancient Indian 

 Village of Morehemoodus, or the "Place of Noises." Almost as noteworthy 

 for its earthquakes as the northern fall line is the central New England coast 

 line, the Boston- August a line, upon which are the prominent earthquake 

 towns of Newburyport and Boston, as well as Pt. Judith, Greenwich, Ports- 

 mouth and Portland. Upon the southern fall line are similarly aligned 

 the earthquake towns of Macon, Clinton, Milledgeville, Saundersville, Au- 

 gusta, Aiken and Columbia. Like the northern fall line this lineament is a 

 boundary between geological formations and is marked by rapids in the 

 rivers which fix the head of navigation. 



It appears from this map of the Atlantic coast region that the lines of special 

 danger from earthc[uakes may not be lines of relief in the surface; and hence 

 in a more elaborate analysis of earthquake shocks the law of the steepest slope 

 is not verified. Yet in many, perhaps in most cases, each seismotectonic line 

 is either in some part of its course or in its extension, a line of considerable 

 slope upon the earth's surface. Thus, for example, the northern fall line is 

 to the southwest of Washington in coincidence with the steep southeastern 

 base of the Appalachian mountain system, the steepest slope within the 

 province studied. The central New England coast line, which at first sight 

 might appear to constitute an exception to the rule, if extended southwest- 

 ward across the continental shelf, is found to correspond in position to that 

 remarkable escarpment which is the border of the continental shelf and on 

 which, for a distance of more than 500 miles the ocean suddenly deepens 

 from less than 1000 to more than 9000 feet. Yet, whether a line of relief 

 or not, each seismotectonic line is throughout distinctly marked in some 

 way, whether as a geological boundary, a straight line of drainage, a fall 

 line, or otherwise. 



De Montessus's law that earthquake shocks are heaviest upon the steepest 

 slopes must therefore be revised, and may be expressed as follows: Earth- 

 quakes are localized upon earth lineaments — faults — and especially at their inter- 

 sections. 



Thus we have learned that earthquakes exercise a selective property by 

 searching out upon the earth's surface the lines of fracture within the dis- 

 trict, and, it would appear, also, that the heaviest shocks are transmitted 

 in the directions of these fractures. Thus the earthquake of October 20, 

 1S70, appears to have been caused by vibrations which were sent out from 

 and transmitted along the principal lineaments of the New England province. 

 The earthquakes of May IS, 1729, Aug. 10. 1884, and Aug. 31, 1886, have all 

 been especially marked in the chain of great cities upon the northern fall line. 



