446 Marsh — Jurassic formation on the Atlantic Coast. 



The origin of Long Island Sound was doubtless largely 

 dependent upon ttie soft Jurassic clays that once filled its bed. 

 The barrier on the north was the rock-bound ^ew England 

 coast essentially as it is to-day. The outer barrier, now 

 removed or beneath the ocean, was perhaps of less durable 

 material, and, as the coast subsided, gradually succumbed to 

 the assaults of Atlantic waves. The great terminal moraine 

 at the close of the glacial period proved a second barrier, and 

 the waters from the melting ice and the larger rivers sought 

 an outlet to the sea, both east and west, and thus a channel 

 was formed in the soft clays and sands that the strong ocean 

 currents gradually enlarged to its present size. 



Conclusion. 



The problem now before us is the presence or absence, on 

 the Atlantic coast, of strata of Jurassic age. The exact posi- 

 tion where such deposits should be found, if present, is well 

 known to all geologists familiar with our eastern border. The 

 fresh- water Triassic beds below this position and the extensive 

 marine Cretaceous above have long ago been carefully studied, 

 and their exact limits defined. 



For many hundred miles, along the line where the Jurassic 

 should occur, there is a well-marked series of fresh-water 

 clays and sands quite distinct from anything else on the 

 coast, and the question is, — are these beds of Jurassic or Cre- 

 taceous age ? The prevailing opinion hitherto has been 

 strongly in favor of the latter, although this view separated 

 two allied fresh-water formations, and still left out the great 

 Jura, so well represented in other parts of the world, and 

 especially in our own Rocky Mountain region. 



How difficult it is to lay aside preconceived opinions, every- 

 one knows. The long supposed absence of the Jurassic on the 

 Atlantic coast seems to have blinded those who had the forma- 

 tion under their feet. Tlie evidence to-day in favor of its 

 presence, if not conclusive at every point, is vastly greater than 

 the opposing testimony. Moreover, its acceptance explains at 

 once a mystery of long standing,^why the records of Jurassic 

 time were not preserved here in their true place. 



To call this peculiar Atlantic formation Cretaceous in its 

 various eastern outcrops, when the western expansion of the 

 same characteristic deposits has been proved Jurassic, is 

 certainly not scientific. To do this in the light of present 

 testimony, including the animal remains, vertebrate and inver- 

 tebrate, the unique structure and materials of the strata 

 themselves, and especially their definite position where the 

 Jura should be, is to violate the laws of evidence. 



