196 POPULAR SCIENCE MONTHLY 



is the Utica slate, near the top of the Ordovician, while between the 

 Potsdam and the Utica appear in order from below, upward, the Beek- 

 mantown, Chazy and Trenton limestones. Except perhaps the Utica 

 slate and the Trenton limestone, which is somewhat shaly, all these 

 are firm, resistant rocks. The visible contacts of the Paleozoic strata 

 with the old crystallines, especially on the northwest and west, are 

 often those of sedimentary overlap, clue to an advancing shore line, but 

 on the east and northeast they are much more frequently due to block- 

 faulting of a most interesting character and exceedingly significant as 

 throwing light on the physiography of the interior mountains. Aside 

 from this, however, the Paleozoic strata enter only in a very minor way 



Fig. 2. Mt. McIntyre, the SECOND Peak in ALTITUDE — viewed from the southeast. 

 The side towards the observer is very steep. 



into the structure of the mountains. They occur around the edges, 

 except for a few isolated outliers from five to forty miles within the 

 Precambrian area. 



After the deposition of the Utica, so far as the actual evidence is 

 concerned, there were no more rocks laid down until the advent of the 

 Labradorean ice sheet of the Glacial epoch. Whether later Paleozoics 

 once existed and have been removed by erosion, or whether the area has 

 been continuously land from the close of the Ordovician to the present, 

 may be esteemed to a certain extent open to debate. From observa- 

 tions near Little Falls on the southern side, Professor H. P. Gushing 

 has concluded that the Niagara limestone probably extended a long 

 distance into the area of the crystallines if not entirely across. But no 

 trace of it has been discovered in place, and the great gap in time from 



