174 loRTY-sixTH Report on the State Museum. 



eastern limits of the state adjoining Massachusetts, Connecticut 

 and Yermont to its western extremit}^ was about twenty-eight 

 inches and its extreme limit from north to south along the 

 eastern counties of the state, or from the Canada line to Sandy 

 Hook was two inches less than its ex:tent from east to west, or 

 twenty-six inches. The location of towns, villages, and post offices 

 were doubtless taken from the best maps extant, but these 

 afforded very unsafe guides for locating the outcrops of the 

 geological formations. 



However, at the close of the survey the order of sequence 

 among the several formations, with the exception of the crystalline, 

 metamorphic and partially altered rocks of the eastern and north- 

 eastern counties of the State, had been determined, and these were 

 laid down upon this map with as much accuracy as the map itself 

 permitted, and this representation has served the purpose of a gen- 

 eral guide to the geological structure of the State of l^ew York. 

 This map is still useful in showing the general distribution of the 

 unaltered stratified rocks of the State, but even before it had been 

 published, the geologists having in charge the eastern portion of 

 the State were not so well satisfied with their work that universal 

 agreement could be had upon certain areas of country and no 

 attempt was made to represent the age and relations of certain 

 of the formations on the east side of the Hudson river. The 

 index or legend, and the colors of the ^rea representing the 

 " primary system,-' were followed by the Potsdam sandstone and 

 thence in regular sequence of the formations from that horizon 

 to the Catskill mountains, or the Catskill group, inclusive. There 

 was no difference in color between the metamorphic rocks of 

 southeastern ^N^ew York and the older gneisses and granites of 

 the Laurentian area of the Adirondacks in the northeastern part 

 of the State, and of the Highlands of the Hudson Kiver. The 

 metamorphic limestones of the southeastern part of the State, 

 now known to be of older age even than the Potsdam sand- 

 stone, were not separated by color from the limestones of the 

 Trenton period and no sandstone older than Potsdam was recog- 

 nized on the map as published in 1842. 



The patskill group in its westerh extension was represented as 

 terminating abruptly and the limits between the formations of 

 Chemung and Catskill were considered as trenchant lines, making 



