588 W. 0. CROSBY 



Construction (accretion) reliefs 



Littoral and fluvial = spits, bars, deltas 



Eolian = dunes 



Glacial = drumlins, moraines, eskers, kames 

 Subterranean Agencies 



Construction (accretion) reliefs 



Igneous extrusion = volcanoes and peleliths 



Igneous intrusion = laccoliths and laccolithic domes 



Aqueous extrusion = tufa cones and terraces 



Aqueous intrusion = crystosphenes and saline domes^ 

 Deformation reliefs 



Plication = anticlinal and monoclinal ridges, domes and plateaus 



Dislocation = block mountains and plateaus 



Hydration and vertical swelling = statenliths and statenlithic domes 



Serpentine is a rock of rather restricted distribution. In 

 Eastern North America it is chiefly confined to the narrow and 

 discontinuous Appalachian belt of peridotite and other basic 

 magnesian rocks (to the alteration of which the serpentine owes its 

 origin) in the western margin of the seaboard zone of crystalline 

 rocks (igneous and metamorphic). In this belt, extending from 

 Newfoundland and Gaspe Peninsula to Central Alabama, the basic 

 magnesian rocks tend to occur in a series of isolated lenses (lentic- 

 ular stocks and dikes) the axes of which coincide with the strike of 

 the enclosing gneiss and schist.^ The Staten Island and Hoboken 

 stocks of serpentine are thus seen to be entirely typical in their 

 structural relations; and it is a legitimate inference from these that 

 all of the stocks in which serpentinization is well advanced are, 

 theoretically at least, statenliths. Many of the serpentine stocks 

 exhibit actual relief, notwithstanding the resistant nature of the 

 inclosing formations; but rarely, probably, is the relief so marked 

 or so sharply defined as in the type example. 



^ A crystosphene, as defined by Tyrell (Journal of Geology, XII, 232-36), is a lens 

 of ice formed in or beneath the tundra of high latitudes and arching up or doming the 

 overlying materials. It is here proposed to broaden the definition to include the saline 

 domes of the Gulf Coastal Plain and, in general, all instances where the surface has 

 been domed by mineral (ice, salt, sulphur, gypsum, etc.) segregation and crystalliza- 

 tion. This appears permissible, since crystosphene may equally well be translated 

 ice-wedge or crystal- wedge. 



^ North Carolina Geological Survey, Vol. I, Plate 4. 



