1883.] 251 [Sharpies. 



I regard these deposits as simply fossil guano which has so 

 long been exposed to the action of air and moisture that the 

 ammonia has almost entirely disappeared. The earth is almost 

 entirely destitute of odor, thus showing the completeness of the 

 decomposition. The absence of recognizable remains is readily 

 accounted for, bones buried in a manure pile quickly lose their in- 

 tegrity and tumble to powder. 



The presence of so much sulphate of lime is more difficult to 

 explain. Professor Dana, in speaking of some similar deposits 

 which contain much sulphate, supposes it comes from the evapor- 

 ation of sea water, as it is a well known fact that when sea 

 water evaporates the first thing deposited is the gypsum. Just 

 how this could have taken place in this instance I am unable to 

 say. The gypsum and other soluble substances can be readily 

 dissolved out of the deposit, as is shown in the guano from one of 

 the caves into which the sea water flows freely. In this cave the 

 guano from under the water contains when dried nearly seventy 

 per cent, of bone phosphate, while the gypsum is quite low. 



The entrance to the second cave that we visited was in a hill- 

 side. At this place we descended over broken rocks to the water 

 level where we found distinct evidence of the ebb and flow of 

 the tide, though the cave is at least half a mile from the shore. 

 We entered a boat and were rowed into the cave for about a 

 hundred yards, through a channel from fifteen to twenty feet 

 wide. By burning magnesium wire from time to time we could 

 get some idea of the size of the cave and could see passages 

 opening off from it on either side. Near the end the cave made 

 an abrupt turn and opened into a large vaulted chamber, 

 about forty feet in height, and fifty feet in diameter; at the 

 apex of the vault there was an opening which admitted the 

 light, so that it was well illuminated. The entire floor of the 

 chamber was covered to the depth of twenty-five feet above 

 water level with guano. It was estimated that there were at 

 least one thousand tons in this one heap. In a side chamber ad- 

 jacent to this one, there was also an opening in the roof through 

 which the fig roots had descended, and we cut one of these and 

 brought it with us as a trophy. It was about three-quarters of 

 an inch thick and over fifty feet in length. The same absence of 

 fossils was observed here as elsewhere. The enormous extent 



