REPORT OF THE DIRECTOR AND STATE GEOLOGIST 



vestige of that old surface now remains. The old lava-filled 

 channels of ascent however are still to be seen, and to such the 

 term " dikes w , is applied. There are two sets of these, corres- 

 ponding to at least two separate periods of intrusion. The lava 

 of the first was fairly acid and gave rise to the red, syenite dikes 

 which are quite numerous on Rand hill, while that of the second 

 was very basic and the source of the black, diabase dikes so 

 common throughout the region. 



Another long period of erosion followed, the region still con- 

 tinuing above sea level, and many hundreds of feet of rock were 

 worn away from the surface. Then 'a slow depression of the 

 district commenced and continued sufficiently long to submerge 

 probably the entire Adirondack tract beneath the waves of the 

 sea. The surface of the sinking land was much more even than 

 it is at the present day, though it still had considerable relief. 

 The stream valleys were well marked and separate by low, 

 rounded hills or ridges. During the long continued erosion 

 period the land must have suffered repeated uplifting in order 

 to permit the removal of so great a thickness from the surface. 



During the first part of the period of subsidence the sea was 

 shallow over the land, and sheets of coarse sand, with much 

 gravel, specially at the base, were laid down. Then, either 

 because more rapid subsidence deepened the sea, or else be- 

 cause the land was so lowered and submerged that it was in- 

 capable of furnishing more detritus, the waters gradually cleared, 

 and the various limestones, Calciferous, Chazy and Trenton, were 

 laid down in the order named as calcareous muds on the still sub- 

 siding sea floor. During the earliest part of this period occa- 

 sional sheets of sand were swept in by currents and alternate 

 with the calcareous layers. During the deposition of the Tren- 

 ton limestone currents washed in a certain amount of fine mud 

 from time to time, from some land area probably to the north- 

 east. This increased in amount, in consequence probably of 

 shallowing and the nearer approach of some land area, and the 

 calcareous muds of the Cumberland head rocks and the black 

 muds of the Utica slate were laid down on top of the limestones. 



