330 University of California Publications in Geology [Vol. 7 



elature I propose that this and similar rocks be known as 

 fanglomeratc. The word is a hybrid and objection will doubtless 

 be made to it on this score. It is, however, a descriptive term 

 with specific connotation as to both the character of the rock and 

 its mode of formation. My purpose in suggesting the term is 

 not so much to amplify the terminology of petrography as to 

 emphasize the geological significance of a class of rocks which 

 have received but little attention. 



Limitations of the Term. — In defining the term I must first 

 make clear that it is not intended to include the finer sediments 

 on the lower flanks of alluvial fans, but only the coarser deposits 

 in the upper part of the embankment. In setting limits of 

 texture or size of grain within which the term fanglomerate shall 

 apply we encountered the same difficulty as in the case of con- 

 glomerate. When the constituent units of a conglomerate are 

 very large the aggregation is often referred to as a "boulder 

 bed"; and when they become small the rock passes insensibly 

 into a sandstone. Barrel 1 in a recent paper 5 places the lower 

 limit of the diameter of pebbles in a conglomerate at 5 mm., 

 but states that common usage places it at about 2 mm. The 

 transitional condition may be, and usually is, designated by 

 various descriptive phrases, there being no hard and fast line 

 between common conglomerate and common sandstone. 



As to the coarseness of texture of fanglomerate there appears 

 to be no convenient upper limit other than that set by nature. 

 In many alluvial fans the constituent blocks are of extraordinary 

 size near the apex, and sporadic blocks several feet in diameter 

 are by no means uncommon far down the slope where the average 

 size of the fragments may be less than an inch. Whether the 

 large blocks be aggregated, or whether they occur more or less 

 isolated in the midst of finer material, they form an integral 

 part of the deposit and are of course included in the term 

 fanglomerate It is evident from this that some of the most 

 interesting fades of fanglomerate cannot be illustrated by speci- 

 mens, and that students will he able to familiarize themselves 

 with them only by field examination. 



•-■Bull. G. S. A., vol. 23, p. 442, 1912. 



