1859.] WOODS TERTIARY ROCKS. 257 



is frequently found immediately over the water-level. Sometimes, 

 however, the flints are white ; but this is seldom the case ; and both 

 black and white varieties contain fossils, most commonly Bryozoans 

 and Sponges. 



It might naturally be expected that in such loose and soft deposits 

 water would more or less undermine the rock and cause subterranean 

 hollows. Accordingly we find that the whole district is more or 

 less honeycombed with caves. Sixteen, and perhaps more, are 

 known, of very considerable extent ; but the smaller ones abound 

 in different localities, confined, however, to the higher ground, or 

 where the country is undulating, for I cannot call to mind a single 

 instance where they have been found on level flats. The most 

 remarkable of all are those situated on a high ridge on the northern 

 side of the Mosquito Plains (see Map, p. 254). There are three very 

 close to one another, the entrance to which is a round aperture, about 

 6 feet wide, on the summit of the ridge on which they occur. The 

 first cave is about 200 feet long, divided into three large halls, from 

 which there are occasional passages leading into extensive side- 

 chambers. At the end of the last cave the passage ramifies into 

 several smaller tunnels, which, though too narrow to admit of actual 

 examination, are supposed to be continued for a long distance. The 

 direction of the caves is nearly north and south, that is parallel with 

 the axes of the ridge. The entrance is at the southern end. At 

 the termination of the first chamber in the large cave, there is a large 

 stalactite, which almost entirely blocks up the passage into the next. 

 At the foot of this, on the side of the entrance, there is a very 

 extensive deposit of bones. These occupy just such a position as to 

 lead one to conclude that they had been deposited from a current of 

 water flowing from the entrance towards the narrow end. To such 

 a stream the immense stalactite would act as a dam, only allowing 

 the water to pass through a narrow passage at each side. 1 must 

 state, however, that there is but slight internal evidence of such a 

 stream, excepting perhaps that the walls of the cave are somewhat 

 undermined all round the first chamber: and a stream running 

 strongly enough to bring down bones might be expected to leave more 

 evident marks of its former existence. But, if a stream did hollow 

 out the caves, there must have been a period during which its How 



was stopped; for the large stalactite hoars evidence of having been 

 formed in small columns at first, and a current of water would have 

 prevented their formation, and have eroded them away much Easter 

 than the drippings from the limestone could repair the damage 

 done. Supposing the great Btalaetite to have been formed during a 



time when water was not running, its existence easily aoCOUntB for 

 the deposit (if hones at its fool : for it WOUld act 88 a harrier to the 

 stream. 

 The banes in question are mostly of extinct species, olosel) allied to 



those of animals a! present inhabiting the locality, hut many times 



larger. The most common are those of a rodenl Bomewhal resembling, 

 in the form of the skull, the dentition, and the markings on the 



molars, our existing domestic Mouse, though it ia many times larger. 



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