184 NEW YORK STATE MUSEUM 



shales now altered to mica schists, argillaceous limestones that have 

 become basic gneisses and amphibolites. as well as pure carbonate 

 materials that are now marbles. The sediments at one time, no 

 doubt, spread over the whole Adirondack region, and the present 

 irregular and patchy distribution is the result of extensive erosion 

 upon the formations which at dilTerent times were also invaded, 

 broken up and to some extent absorbed by the great igneous masses 

 which came up from below. 



The metamorphosed sediments exhibit very similar features and 

 relationships wherever found in the x\dirondacks, so that they are 

 regarded as members of a single geologic series, which is called the 

 Grenville series from their analogy with the Canadian formations 

 that bear that name. Little is known as to their time-relations 

 beyond the fact that they antedate all the other Adirondack rocks, 

 and consequently must have been laid down very early in the Pre- 

 cambric period. Subsequent to their deposition, but before the 

 opening of Camhric time, there was a long era characterized by 

 intervals of great igneous activity in which granite, .anorthosite, 

 syenite, ga'bbro and finally diabase were erupted. None of the mem- 

 bers of the Grenville carries recognizable fossil remains, though the 

 abundance of graphite in some of the strata, particularly the quartz- 

 ites, leads to the inference that life existed at the time. 



In most of the belts the limestones and the accompanying schists, 

 quartzites and gneisses are tilted and present their upturned broken 

 edges at the surface. The angle of inclination is usually high, 

 dips of less than 30° being exceptional, whereas a nearly vertical 

 attitude is quite common. The strike is nearly always between 

 the north and easterly compass points, in most cases nearly north- 

 east, but is subject to local variations. The beds over large areas 

 may maintain monoclinal arrangement, with the inclination in the 

 same direction ; this is the common condition in fact, as few in- 

 stances have come to notice where the dips of adjacent belts are 

 in opposite directions. The general high inclination and the pres- 

 ence of minor folds seem to indicate, however, that the beds are 

 not simply tilted up by a great monoclinal flexure, but that they have 

 a much more complicated structure through the presence of anti- 

 clinal and synclinal folds strongly compressed. The actual rela- 

 tions that exist in any of the belts can not be stated at the present 

 time, and it is still uncertain just what the order of the sedimentary 

 succession may be. 



The St Lawrence county belts are much broken by irruptive 

 masses, of mainly granitic nature. These rocks have a massive to 



