954 STUDIES FOR STUDENTS 



B. Beyond the edge of the ice^ on land. — As the waters escap- 

 ing from the ice flowed farther, deposits of stratified drift were 

 made quite beyond the edge of the ice. The forms assumed by 

 such deposits are various, and depended on various conditions. 

 Where the waters issuing from the edge of the ice found them- 

 selves concentrated in valleys, and where they possessed sufifl- 

 cient load, and not too great velocity, they aggraded the valleys 

 through which they flowed, developing fluvial plains of gravel 

 and sand, which often extended far beyond the ice. Such fluvial 

 plains of gravel and sand constitute the valley traiiis'' which 

 extend beyond the unstratified glacial drift in many of the 

 valleys of the United States. They are found especially in 

 the valleys leading out from the stouter terminal moraines of 

 later glacial age. From these moraines, the more extensive 

 valley trains take their origin, thus emphasizing the fact that 

 they are deposits made by water beyond a stationary ice margin. 

 Valley trains have all the characteristics of alluvial plains built 

 by rapid waters carrying heavy loads of detritus. Now and 

 then their surfaces present slight variations from planeness, but 

 they are minor. Like all plains of similar origin they decline 

 gradually, and with diminishing gradient, down stream. They 

 are of coarser material near their sources, and of finer below. 

 Such stratified drift, which constitutes a distinct topographic, 

 as well as genetic type, is well known, and further description 

 or discussion is unnecessary. 



Where the subglacial streams did not course through sub- 

 glacial valleys, they did not always find valleys at hand upon 

 their issuance from the ice. Under such circumstances, each 

 heavily loaded stream coming out from beneath the ice must 

 have tended to develop a plain of stratified material near its 

 point of issue — a sort of alluvial fan. Where several such 

 streams came out from beneath the ice near each other for a 

 considerable period of time, their several plains, or fans, were 



' For fuller definition and illustration of valley trains see Chamberlin, 3d Ann. 

 Report U. S. Geol. Surv., p. 302; Journal of Geology, Vol. I, p. 534. Salisbury, 

 Report of the State Geologist of New Jersey, 1892, pp. loa-ic. 



