46 NEW YORK STATE MUSEUM 



was effected before the ocean came back. But land detritus seems 

 by this time to have been largely exhausted or the rivers turned 

 elsewhere, for great beds of nearly pure magnesian limestone, the 

 Ogdensburg, now accumulated, Cryptozoon reefs grew widely and 

 a normal marine fauna of molluscs and brachiopods thrived. Yet 

 in the very midst of these limestones an occasional thin bed of pure 

 sandstone marks a sudden flood or sweep of current, and upon each 

 such sand waste a new Cryptozoon colony sprang up. 



The continuation of the Paleozoic sedimentary record lies north- 

 ward (see the key map, figure i) across the St Lawrence. Here 

 we find evidence of further oscillations,^ the Chazy limestones with 

 a basal (Aylmer) sandstone resting upon eroded surfaces of the 

 Beekmantown, while above these follow the Black River and Tren- 

 ton series of limestones and calcareous shales. Whether the Chazy 

 beds ever reached into our quadrangle is unknown. If the Trenton 

 mass at Mr Veitch's (see page 39) is a true outlier, then deep erosion 

 of the Beekmantown dolomites was proceeding in our area during 

 Chazy and Black River time; and the Trenton sea transgressed 

 over the beveled edges of the Chazy and Ogdensburg strata, already 

 arched into the undulations of today, and laid its sediments down 

 upon those of the Tribes Hill division and possibly on still lower 

 beds. 



After the completion of sedimentation in our region, or perhaps 

 (if the preceding is correct) immediately at the close of Beek- 

 mantown time, the rocks laid down in originally horizontal strata 

 were thrown into the gentle undulations they now exhibit. This 

 movement may not have been single and simple. More likely it was 

 renewed from time to time with each doming of the Adirondack 

 massif, and perhaps in slightly different directions. The total 

 result, conditioned in part by the belted and uneven Precambrian 

 floor, is complicated, and by the drift covering rendered most per- 

 plexing. The colored cross sections show diagrammatically (with 

 a vertical exaggeration of eleven times) the simplest possible inter- 

 pretation of the observed data. Southward, in the Potsdam out- 

 liers, the amount of compression becomes clearly greater, perhaps 

 because in part referable to a disturbance older than the upper 

 white sandstones (see page 44), but also in part involving these 

 (as at locality 75). The colored cross section at locality 80 



* Consult N. Y. State Mus. Bui. 145, p. 17-20; Geol. of Can., p. 123-97; 

 G. S. of Can. Rep't, for 1899, vol. 12, n. s. (1902), Rep. G, J; Am. Jour, of 

 Sci. (1905) 20:353-66. 



