EYIDENUE FROM OOXULOMERATES. 59 



Tlie hypothesis that tlie conghniierntes of the Cambrian and Carhon- 

 iferons as exhibited in tliis loeahtv are the resuhs of ylacial action is sup- 

 })orted by the general distribution of such deposits in tliis and <^tlier 

 countries. ]\Iassive con<>h>]nerates of o-reat areal extent are (hstinctlv more 

 common in liigh than in \cy^y hititudes. With rare, find in most cases 

 questionable, exceptions tlie deposits of this nature wliicli can be trailed 

 horizontally for a OTeat distance from north to south fade awa^^ as thev 

 approach the eqiuxtor. As our study of conglomerates a<lvancesy more of 

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

 pebbles. The great eiaiglomerates at the 1)ase of the Carl)oniferous hi 

 India, which from their interstratifiied position appeared not to 1)e open to 

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

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

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

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

 contain. 



Although this is not the place for an extended discussion of tlie mattei', 

 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. 



KECOM) VATATE OF C^OlSTGIiOMERATES, 



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 the}" 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 iipon 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 tlie rocks whence they 

 came at the time the pebbles were brought together. 'J'liis evidence, 



