EVIDENCE PEOM CONGLOMERATES. 59 



The hypothesis that the conglomerates of the Cambrian and Carbon- 

 iferous as exhibited in this locality are the results of glacial action is sup- 

 ported by the general distribution of such deposits in this and other 

 countries. Massive conglomerates of great areal extent are distinctly more 

 common in high than in low latitudes. With rare, and in most cases 

 questionable, exceptions the deposits of this nature which can be traced 

 horizontally for a great distance from north to south fade away as they 

 approach the equator. As our study of conglomerates advances, more of 

 the deposits are found to afford evidence as to the glacial origin of their 

 pebbles. The great conglomerates at the base of the Carboniferous in 

 India, which from their interstratified position appeared not to be open to 

 the explanation which has been advanced in this writing, have recently 

 afforded clear evidence to show that glaciation, possibly occurring at a 

 time when the area was elevated to a great height above the sea, suffi- 

 ciently accounts for the origin of the pebbles and bowlders which the beds 

 contain. 



Although this is not the place for an extended discussion of the matter, 

 it may be worth while to remark that a collation of the recent studies on 

 conglomerated deposits clearly shows that we are fast approaching the 

 point where beds of this nature will be taken as presumptive evidence of 

 glacial action occurring- at the time of their deposition, or perhaps imme- 

 diately preceding it. 



RECORD VALUE OF CONGLOMERATES. 



In connection with these considerations relating to conglomerates, it 

 may be well to note that deposits of this nature have another much neg- 

 lected element of value to the geologist, in that they afford him an opportu- 

 nity to ascertain many facts concerning the physical conditions of the region 

 in which they occur at the time of their formation. Although the value of 

 these indications is in good part self-evident, they have been so generally 

 neglected that it is worth while to dwell upon the methods of using them 

 and to illustrate them by a special study of the Narragansett field. 



If a conglomerate has not been subjected to metamorphic action 

 sufficient to change the original character of its pebbles, these fragments 

 may be taken as evidence concerning the state of the rocks whence they 

 came at the time the pebbles were brought together. This evidence, 



