254 On the Geology of the Key of Sombrero, W. I. 



Martin, about forty miles distant, the latter having been noted 

 by a resident in the town of Philipsburg. 



Date. 



Sombrero. 



1861 

 1862 



1863 



1864 



1.30 a.m. No sound. 

 1.45 a.m. "A smart shock." 

 4.45 a.m. " A smart shock." 

 Night. No shock felt. 

 1.10 p.m. " A smart shock." 

 2 a.m. " A slight shock, accom- 

 panied with a loud and long 

 roaring noise." 

 10 a.m. "A smart shock." 

 5 p.m. " A slight shock." 

 11.30 a.m. "A slight shock, 

 accompanied with a loud and 

 long roaring noise." 

 8 a.m. and 11.30 a.m. Two 

 slight shocks. 



Subterranean sound. 

 2 a.m. Sharp shock. 



No shock felt. 



Sharp shock. 

 1 p.m. Strong tremor, 



No shock felt. 



No shock felt. 



Similar observations have been recorded by Schomburgk, 

 concerning two islands of the Virgin group, which are only 20 

 miles apart. 



Date. 



Tortola. 



Anegada. 



1830 

 1831 



Oct. 

 Apr. 23 



Heavy shock. 

 No shock felt. 



No shock felt. 

 Shock. 



§ 5. Beds. — This whole formation consists of a series of beds 

 of limestone, intersected by veins of successive periods contain- 

 ing a greenish clay and varieties of rock-guano. Its history is 

 naturally separated into two eras. In the first occurred the 

 deposition of corals, shells, and sand, in mid-channel, upon the 

 surface of an oscillating shoal, the oscillations being principally 

 submarine. In the second, the surface rarely subsided below 

 the sea-level, and the depositions (guano, etc.) were derived 

 only in part from the sea. In this paper we shall have only 

 the former to be particularly discussed. 



That part of the Key which has been the least affected by 

 denudation (the southern level), consists of six beds of limestone. 

 A geological map of the Key, from which the extent of the denu- 



