SANDSTONE DIKES OF UTE PASS. 143 



complementary faults have settled down relatively to the 

 bordering masses, bearing with them their loads of Pots- 

 dam sediment. The very moderate thickness of the 

 Potsdam beds (40 to 50 feet) would seem to set a corre- 

 spondingly narrow limit to the depth of these wide dikes ; 

 and yet some of them actually outcrop in such strong 

 relief as to prove a depth of several hundred feet at least. 

 Escape from this dilemma is aftbrded, however, by the 

 reasonable supposition that the sandstone was sufficiently 

 unconsolidated to flow under the great pressure to which 

 it was exposed ; and also by the facts noted in the great 

 dike on Sutherland Creek, where the sandstone, still 

 distinctly bedded, has been strongly folded and tilted to 

 a vertical or overturned position (Fig. 3). Compression 

 between converging walls of granite might, obviously, 

 increase the vertical thickness of the sandstone to almost 

 any extent. An actual flowing of the sand into the chasms 

 opened beneath it is plainly indicated in the case of all 

 the narrower dikes and dikelets and their intricate 

 branches. 



Of course it is a logical though by no means a neces- 

 sary deduction from this theory that some of the sand- 

 stone dikes should break the granite-Potsdam contact, 

 disturbing: or obliteratinij the bedding of the sandstone. 

 No undoubted instances of this have been observed in a 

 somewhat thorough examination of this contact throughout 

 the Manitou area, Imt it is not impossible that they exist. 



Concerning the geolosrical age of the sandstone dikes 

 no positive statements are warranted by the facts now at 

 our conmiand, although the explanation of the dikes here 

 proposed aflbrds us a clue, since they must be coeval with 

 the Ute fault. This displacement was certainly not com- 

 pleted until Post-Cretaceous times, but it may well have 

 begun at a nmch earlier period, since, as Cross has stated, 



