62 REPORT — 1902. 



referred to by its numbers in the Shide register — for the records obtained 

 in the years 1900 and 1901. An attempt has been made to place these earth- 

 quakes in groups, each group being enclosed by a dotted line. Altogether 

 there are twelve such groups which on the map are indicated by the tirst 

 twelve letters of the alphabet. A glance at this map shows that certain 

 of these groups, like B and C, overlap, whilst there are many instances 

 ■where origins are placed outside the boundaries of any of the groups. 

 It is therefore likely that whea the data on which these groupings are 

 based become more complete the same will be subjected to modifications. 

 The large numerals indicate the number of earthquakes which originated 

 in the districts marked A, B, C, &c., in the years 1899, 1900, and 1901. 

 The notched bands give the direction of prominent ridges on the face of 

 the »lobe, whilst the dotted areas are the ' deeps ' or depressions in the 

 beds of various oceans exceeding 3,000 fathoms in depth. 



That there is a relationship between the distribution of the origins of 

 large earthquakes and the pronounced irregularities on the surface of the 

 earth will be seen from the following notes. 



A. Alaskan Region (number of earthquakes 25). — The average depth 

 of the water in this bight is about 2,000 fathoms, but in its northern 

 part depths of 2,200 fathoms have been found within sixty miles of 

 the shore. On this shore Mount St. Elias rises to a height of 18,000 

 feet. An average slope from the land to the sea on a north south line 

 can be found which exceeds 100 feet per mile. This is over a distance 

 of 180 miles. 



On the face of this and neighbouring slopes during the last three years 

 it is probable that molar displacements of great magnitude have taken 

 place. On September 10, 1899, in the island of Kanak, opposite Yakuta, 

 a graveyard sank so that on the next day a boat was able to row over 

 the place where it had been, and the tops of the submerged trees could be 

 seen. Many of the earthquakes from this region have yielded large 

 seismograms at the Cape of Good Hope, which is antipodean to Alaska. 

 We have here a district partly belonging to the Alutian ridge, off the 

 southern shores of which within eighty miles of land depths of 4,000 

 fathoms have been noted, where orogenic processes are now marked the 

 extent of which will probably be gauged by future soundings. 



B. Cordillerean Region (number of earthquakes 14). — This region 

 forms the western side of the Mexican plateau and the Cordilleras. Just 

 south of the 20° parallel a depth of 2,800 fathoms has been found within 

 forty miles of the shore, whilst depths exceeding 2.000 fathoms have been 

 found a little over 100 miles from the land, somewhat farther to the south. 

 Although thei-e are peaks in these regions rising to heights close upon 

 18,000 feet, the average height of the ranges does not greatly exceed 

 6,000 feet. There are, therefore, in this region slopes of 180 to 570 feet 

 per mile, and the instability of these is testified by the frequency of 

 their yieldings. 



C. Antillean Region (number of earthquakes 16). — Here we have at 

 least two ridges to consider — that of Cuba, Haiti, and Puerto Rico 

 running east and west, and that of Grenada, St. Yincent, Martinique, 

 Dominica, and other islands running north and south. The east-west 

 ridge slopes steeply to the north into water which north of Puerto Rico 

 attains a depth of 4,000 fathoms, and to the south into water 2,500 fathoms 

 in depth. These depths are respectively found at distances of sixty and 

 forty miles off land and indicate slopes of 400 and 375 feet per mile. With 



