THE JAMAICA EARTHQUAKE 401 



the River Cobre to the carriage road. From soundings taken by the 

 kindness of Mr. Charlton Thompson, harbor master, it was ascertained 

 that in several places along the edge of the harbor, the bottom had 

 sunk from old soundings of a fathom and a half to over six fathoms, 

 and that on the harbor side of the base of the Palisadoes a series of 

 step-faults reached a maximum depression at the shore to the north 

 of four fathoms (Figs. 12 and 13). This zone of disturbance con- 

 tinued, as far as could be traced, in an interrupted line along the 

 Palisadoes, and caused a maximum depression at the western tip of 

 Port Royal, where the buildings were tilted by the sinking and a hun- 

 dred yards or more of land were submerged to a depth of from eight 

 to twenty-five feet (Figs. 14-16). This Assuring of the earth was 

 caused by the repeated tearing apart and closing of the earth's crust, 

 accompanied generally by the ejection of water, sand and mud, some- 

 times to the height of three or four feet, but the subsidence prevented 

 the forming of any cones about these craterlets. The sands first thrown 

 up were afterwards covered by a layer of mud. 



To account for the unique line of Assuring and subsidence is diffi- 

 cult. It was noted that considerable disturbance took place at the 

 shore line where the earth vibrations were refracted in changing from 

 the medium of one elasticity to a medium of a different elasticity. 

 But the middle portions of the harbor were stable and the channel was 

 unchanged, though a beacon light near Fort Augusta was broken off. 

 In this limestone country, solution by underground waters might be 

 sufficient to account for the sinking of a small area like the harbor ac 

 Kingston. But the harbor did not sink — only a small encircling zone, 

 and that located either on the shore or slightly offshore. The con- 

 tinuous tearing apart and closing of these fissures, covering a few 

 hours' time as it did in some instances, might account for the 

 hydraulicking of the loosely compacted sands and gravels in the zone 

 of Assuring, and allow subsidence. Again, ground-waters may have 

 caused considerable solution of the limey constituents where the waters 

 entered the harbor. No theory as yet satisfactorily accounts for this 

 peculiar subsidence. At the eastern end of the harbor at Rock Fort a 

 considerable change in underground drainage was observed, where a 

 small spring was increased to a stream eight feet wide and six inches 

 deep. 



It was here at the Rock Fort penitentiary quarry that a guard gave 

 me the only reliable account of a sea wave. After a few moments 

 had elapsed and the convicts had run from the landslides on the face 

 of the quarry and gathered around him for protection, the sea retreated 

 for a hundred feet and then advanced inward upon the shore about 

 sixty feet in a low wave a couple of feet high. Ocho Rios, near 



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