24 BULLETIN OF THE 



Discussion of the Evidence afforded by the Attleborough 



Series. 



The facts as given above concerning the rocks of the Attleborough sec- 

 tion and the neighboring parts of Rhode Island carry our information con- 

 cerning the condition of the Atlantic coast line much further than might 

 at first sight be supposed. In the first place, they prove that the Atlantic 

 coast line was during the Cambrian period not far removed from its pres- 

 ent position. The great thickness and general character of the conglom- 

 erates appear to me to be abundant evidence on this point. Whether the 

 formation of these conglomerates was due to glacial action or not, it is 

 clear that they were deposited near the coast line. Only by the action 

 of water moved by strong currents could we have had the stratification 

 induced which appears in many of these pebbly sections. Such rapid 

 movements of water are only possible in shoal regions. The fact that 

 the pebbles have apparently all been derived from rocks in the immedi- 

 ate neighborhood, those which lie to the westward of the Cambrian 

 deposits, indicates that, while the Cambrian region was sea, the neigh- 

 boring district was in a condition to yield detritus to erosive forces, and 

 was therefore presumably laud. We thus fix the marine shore line of 

 the continent in this area close to the present coast. 



It may be here remarked, in passing, that we have now determined 

 four stages in the history of this part of the continent, in which the 

 coast line was near its present position. These are as follows : the 

 Cambrian, which we are now considering, the Carboniferous, which 

 immediately succeeds it in the same field, the Triassic conglomerate of 

 the Connecticut valley, and the probable Miocene conglomerates which 

 appear at Gay Head on Martha's Vineyard. There are two other hori- 

 zons pretty well determined in which fragmental materials formed along 

 the coast line exist, viz. that of the Roxbury puddingstone, which prob- 

 ably belongs in the Cambrian age, possibly in the horizon of the Para- 

 doxides beds, and the coarse sandstones of Cretaceous age which appear 

 on Martha's Vineyard. If we add to these the glacial conglomerate of 

 the last ice period, we have a total of seven stages in the earth's his- 

 tory from the Lower Cambrian to the present day, in which the shore 

 of the continent has appeared near its present position. When we re- 

 member the amount of evidence going to show great erosion in this 

 field since the earliest geological ages, an erosion which may have re- 

 moved the evidence of coast line deposits of many difi'erent ages, we 

 are struck with the fact that we have here proof as to the permanence 



