448 DONALD C. BARTON 



disintegrated material. The arkose is composed of the constituent 



minerals of the granite or gneiss in essentially their original propor- 

 tions. Some of the silicates, especially the biotite, hornblende, and 

 plagioclase, are in many cases highly decomposed. The constituent 

 grains are angular. The upper part of the arkose may show a 

 rude stratification and may grade upward into a well-stratified 

 deposit. The lower portion is massive and grades downward into 

 the granite, and may show the unaltered cores of bowlders of exfolia- 

 tion. 



A good example of this type of arkose is to be found in the lower 

 arkose in the Silurian at Littleton. New Hampshire. Between the 

 Niagaran Limestone and the granite there is from two to eighty 

 feet of arkose which is coarse and granitic in appearance. The 

 quart.: and feldspar are the same as those of the underlying granite 

 and are present in practically their original proportions. There is a 

 slight amount of grained dark matrix. In its upper portion, 



the o shows faint traces stratification and in its lower 



portion it grades into the underlying granite-gneiss. Locally the 

 original spheroidal weathering and the unaltered cores and shells 

 of concentric weathering are distinguishable. 



To this type of deposit are to be referred: 



the Vermont formats rian), Mass 



\ ermont 



- Silurian' 1 .-. . V shire 



Pk . - d part] of the Cobalt District, Onl 



St \ nagansel B sin Massachus - R -'and 



V - Ls Eg 



D. SI HM LKY 



- gnif E arkose in brief, then, varies from 



id cannot be limited in the general statement 



a special set of i ns. Each deposit is sig- 



tditions and these in many a - - 



determined from the individual deposit or its associations. 



In the y g scuss - attempt has o made to show a 



these in conformity wit] otic classification 01 



i type of which is significant of some special tyr. 



