164 NEW YORK STATE MUSEUM 



here shown presents some nearly horizontal joints which curve up 

 southerly and cross the beds. The block here has been subjected 

 both to a strong uplift and to a thrust toward the south. The in- 

 dications of vertical and lateral displacement make it quite possible 

 that these aberrant caverns are also following some preexisting 

 planes of fracture, and that they are in their origin not essentially 

 different from the caves first mentioned. The other cave mouths 

 which show on this plate illustrate clearly the tendency to acquire 

 verticality. 



Now numerous as these joint caves are, they are found with a 

 single exception where the present water line of Lake Champlain 

 either just keeps them covered or cuts across their mouths during 

 some portion of each year. The high water level of spring leaves 

 but comparatively few of them uncovered, but the number brought 

 into view rapidly increases with the lowering of the water level. In 

 other words, the floors of all but a very small number of these 

 caves lie a meter or more below the present low water level of the 

 lake while their roofs stand at varying hights above this level, some 

 of them reaching far above that of present spring floods. Their 

 horizontal depth is not so easily measured but many small mouths 

 give forth deep bass notes when any sea is running and their boom- 

 ing may be heard for considerable distances. A few can be fol- 

 lowed into the cliff for several meters but a narrower portion may 

 be always seen to penetrate to still greater depths. Plate 5 shows 

 a sink hole many meters from the shore line and the sink • hole 

 shown in plate 6 is 150 meters from the nearest lake margin. 1 



J The sink holes shown in plates 5 and 6 both seem to be of com- 

 paratively recent origin. In plate 5 a border of fresh earth, on which 

 nothing was growing, is to be seen around the front of this opening. 

 This feature and the overhanging sod at the left are indications of the 

 removal of much earth in a single season. If anything like an equal 

 amount has been washed out each season the sink hole can not be many 

 years old. That it was covered in comparatively recent times is also 

 shown by the presence of portions of old stumps and roots on the rock 

 surface of the more distant border of the pit. It does not seem likely 

 that we are here dealing with a recently fallen rock roof but it does 

 seem likely that such a roof was crushed in during the last stages of 

 the ice sheet and that the opening was then filled with till and after- 

 ward covered by Pleistocene deposits. As soon as the present land had 

 lowered sufficiently to allow waves to run in and out of the cluster of 

 narrow caves here seen to connect this pit with the lake, the water 

 would undermine and carry away these deposits and so allow the sur- 

 face to finally cave in. Such a conclusion would make the caves con- 

 necting this pit with the lake, preglacial. 



