62 NEW YORK STATE MUSEUM 



pebbles or boulders scattered through its mass, it is known as boulder 

 clay or till. The pebbles or boulders of the till are commonly faceted 

 and striated as a result of having been rubbed against underlying 

 rock formations. Such ground moraine deposits are exceedingly 

 widespread throughout the Adirondacks. 



An interesting type of glacial deposit is the dntmlin which is, in 

 reality, only a low, rounded hill of ground moraine material or till. 

 These are practically unknown in the Adirondacks, though some 

 excellent examples occur on the southern border in the vicinity of 

 Gloversville (Fulton county). 



Glacial boulders, or so-called erratics^ have already been referred 

 to. They are simply blocks of rocks or boulders from the top of the 

 ice or within it which have been left strewn over the country as a 

 result of the melting of the ice. They vary in size from small 

 pebbles to those of many tons weight and are naturally most com- 

 monly derived from the harder rock formations. Erratics are very 

 numerous throughout the Adirondacks. They are most numerous 

 on the lower lands, though by no means rare on the mountains. 

 Sometimes they have been left stranded in remarkably balanced 

 positions. The writer has frequently noted boulders and pebbles of 

 Potsdam (Cambrian) sandstone, derived from the St Lawrence 

 valley, at altitudes of from 3000 to 4000 feet in the central and east- 

 central Adirondacks. Boulders of anorthosite from Essex county 

 are not rare at the southern border of the Adirondacks. 



Another type of glacial deposit in the low hill or hillock form is 

 the kame which, in contrast with the drumlin, always consists of 

 stratified (water-laid) material.' Kames are seldom as much as 200- 

 feet high, and typically they have nearly circular bases though fre- 

 quently they are very irregular in shape. At times they exist as 

 isolated hills or in small groups, but often they are associated with 

 the unstratified morainic deposits. They were formed by debris- 

 laden streams emergmg from the margin of the ice, the water some- 

 times having risen like great fountains because of pressure. Such 

 deposits are now in process of form.ation in Alaska. Kames are 

 very common in the Adirondacks. 



The esker also consists of stratified glacial material, but it is in 

 the form of a low, winding ridge formed near the ice margin either 

 by subglacial streams or in cracks in the ice. Eskers may occasion- 

 ally be seen in the Adirondacks, an exceptionally fine one having a 

 highway at its summit in Thirty-four marsh just east of Blue Aloun- 

 tain lake. Another fine one, about a mile long, lies just west of' 

 . Schroon Lake villas:e. 



