:>S I'HOCKKDINC.S OK TJIK ANN AHBOK MKETING 



juul iiulk-ato. fnrtlieniu)re. a lar.ixe (l(»veU)itiiu>nt of swanii) ami pond conditions 

 under a normally humid climatic condition." -'" 



One thesis in rooard to tlie red color of some rocks defended by Barrell 

 will be noted. He says regard in o' ferric oxide, to Avhich the red color of 

 sedimentary rocks is due: 



"Spontaneous dehydration, assisted by heat and favored by time, does not 

 appear, however, to be the sole cause of the ijreat contrast in color between the 

 consolidated and the surtical ferruirinous sediments. A still more potent cause 

 exists in the dehydration effected by the great increase in pressure and mod- 

 erate rise in temperature which take place upon the burial of the material to 

 some thousands of feet beneath later accumulations.'' -' 



The presence of feldspar particles in sediments that have been trans- 

 ported considerable distances is advanced as evidence of a semi-arid cli- 

 mate, for it "indicates a notable degree of physical, as contrasted to 

 chemical, weathering in the regions of erosion.'^ -- This criterion is a 

 decidedly vahiable one. 



He says: 



"An examination of the character of the matrix or associated line beds is 

 of importance in determining the climatic conditions attending the origin of a 

 terrestrial conglomerate ov sandstone. . . . The character of this fine fluvia- 

 tile or wash detritus in tJic rnjioii o/ its orii/iit may. therefore, be taken as an 

 index of climate. The size or abundance of the coarser material, on the other 

 hand, forms a measure of the rapidity of erosion, and roughly of the degree 

 of topographic relief." -" 



As a part of Barrell's studies of the value of criteria, it will be noted 

 that he dissented from certain of Grabau's opinions regarding the value 

 of overlaps. He says : 



"From these examples it is seen that overlap away from the source of supply 

 can not be used as a criterion of continental or marine origin, any more than 

 transgressive or regressive overlap, but may be due to regional subsidence or 

 tilting or a climatic change which shifts clastic material of a certain kind 

 progressively farther from the source of supply.''-* 



The Interpretation of particular geologic Formations 



Barrell worked from the concrete to the abstract and from the abstract 

 to the concrete. He began by the consideration of specific phenomena. 



-•"Bun. Geol. Soc. Am., vol. 23, 1912. pp. 422. 423. 



-' Jour. Geol.. vol. 16, IOCS, p. 288. 



-'- Origin and significance of tbe Mauch Chunk shale. Bull. Geol. Soc. Am., vol. 18, 

 1VK>7. p. 470. 



^Jour. Geol., vol. IG. 1908. p. liS2. 



-* Criteria for the recognition of ancient delta deix)sits. Bull. Geol. Soc. Am., vol. 23, 

 1912, p. 395. 



