July 20, 1900.] 



SCIENCE. 



83 



have met with encouragement, but the 

 great discoveries remain for the future, be- 

 cause as yet the evidence is meagre and 

 amounts to little more than a stimulus for 

 later work. 



And yet despite the lack of organisms, 

 the elucidation of the genetic and structural 

 problems supplied by these ancient sedi- 

 ments is of the highest interest and impor- 

 tance. They carry us ever farther and 

 farther back toward the primeval conditions 

 on our planet, and year by year the circle 

 of the recognized Algonkian closes in on 

 the admissible Archean, and year by year 

 the ancient gneissic areas yield up the 

 secrets of their pedigrees. 



Not all the sedimentary rocks, once re- 

 garded as pre- Cambrian, have proved to be 

 such on investigation. In many localities 

 metamorphic schists, once supposed to be 

 very ancient, have been safely lodged in the 

 Paleozoic fold, but many more remain and 

 there will be no lack of material for the 

 next generation of geologists to work upon. 

 In all the advances, methods of observation 

 and interpretation have been developed, 

 and the results gained in one locality have 

 been of the greatest service in another. In 

 the Highlands of Scotland, under the guid- 

 ance of Peach and Home, we have learned 

 the part that overthrust faults may play 

 and have realized the complex, although 

 not quite hopeless, aggregate of tangled 

 strata which may result. In the Lake 

 Superior region, Irving and Van Hise 

 and their co-laborers have developed the 

 methods applicable in a region, folded in a 

 complicated way and more or less meta- 

 morphosed, although not faulted. In the 

 Green Mountains, Pumpelly, Dale and 

 others have dealt with folds, metamorphism 

 and faults, all three. In ISTew Jersey, 

 Nason and Wolff have attacked the old 

 gneisses, worse subjects for stratigraphical 

 elucidation than any yet cited, except the 

 Scotch, and "Wolff has appealed with much 



if not conclusive success to inconspicuousi 

 although fairly persistent bands of peculiar 

 rocks to indicate traces of a sedimentary 

 succession. Adams, in the crystalline areas 

 of Quebec and Ontario has dealt with prob- 

 lems more like those which we are to pass in 

 review to-day than are any of the localities 

 mentioned above. They involve the most 

 ancient gneisses, the crystalline limestones, 

 the vast intrusions of plutonic eruptives, 

 and the same dynamic metamorphism ; but 

 there is one important factor in the Cana- 

 dian area which we probably lack in the 

 Adirondacks, and that is the most an- 

 cient gneiss, there called the Ottawa. At 

 least we doubt if its equivalent occurs any- 

 where south of the international boundary. 

 With the crystalline limestones and their 

 associates in the Grenville and with the 

 Norian intrusives, however, we have much 

 in common. 



Outline of the Adirondacks. — The Adiron- 

 dacks — under which term I include the 

 crystalline rocks of northern New York — 

 cover about 12,500 square miles. In out- 

 line the area is somewhat like a circle, that 

 has been flattened on the East along Lake 

 Champlain, and pulled out to a cusp on the 

 West toward the Thousand Islands. The 

 diameter is very nearly 125 miles. The 

 surface consists almost entirely of crystal- 

 line rocks, for, although a few outliers of 

 Upper Cambrian and Ordovician beds are 

 known as much as 40 miles from their 

 parent masses, they are an insignificant 

 fraction of the whole. In the area of the crys- 

 tallines, metamorphosed representatives of 

 both sedimentary and igneous originals are 

 present. All except the small trap dikes 

 have suffered severely from dynamic proc- 

 esses, sometimes to an extraordinary de- 

 gree, and in instances the sediments are to 

 be hardly if at all recognized as such . Suffi- 

 ciently numerous examples, however, re- 

 main which can with certainty be referred 

 to their originals, and great probability for 



