Ailing — Problems of Adirondack Precambrian. 55 



and constitute one of the most difficult problems of the 

 Adirondacks. 



It was Cushing 10 who first pointed out the fact that in 

 Franklin and Clinton Counties para- and orthoschists and 

 gneisses occur that are apparently distinct from the 

 Grenville but earlier than most of the igneous rocks of 

 the region. To this group of doubtful rocks he applied 

 the term "Dannemora formation,' ' from Dannemora 

 mountain in Clinton County, suggesting its equivalency 

 with the " Ottawa' ' gneiss of Canada. Since a possible 

 confusion might arise with a noted Scandinavian locality 

 the name Saranac formation was later substituted. The 

 detail mapping of the Long Lake quadrangle 11 was done 

 some time after the bulletin on the northern Adirondack 

 Region was published. In the latter work Cushing sub- 

 divides the doubtful gneisses into two categories : the 

 "Long Lake gneiss" and the "Grampus gneiss." From 

 Cushing 's description of the Long Lake gneiss it is evi- 

 dent that it is the ancient granite, that he later assigned 

 to the Laurentian, with the associated metagabbro chiefly 

 as inclusions. Recent work would thus remove the Long 

 Lake gneiss from the doubtful rocks. In the Grampus 

 gneiss we find a "grand mixture" of puzzles. A black 

 and white rock is described. "These rocks have the 

 mineralogy of gabbros and diorites, but the field appear- 

 ance is often suggestive of a sedimentary origin. There 

 is often a strong resemblance to the rock . . . which 

 Kemp has described as the 'Whiteface' type of anortho- 

 site." There are red acid gneisses which Cushing thinks 

 form the wall rock of many of the nontitaniferous mag- 

 netite deposits. In addition there is "a peculiar granitic 

 rock . . . difficult to describe, though easy to recognize 

 ... it occurs in a great number of Grenville sections, 

 lying in among the sediments, or cutting them out, both 

 above and below. ' ' 



While it is possible that some of the individual phases 

 of these rocks so designated may turn out to be some one 

 or other of the well recognized rock units, yet it is con- 

 ceivable that there are rocks in the Adirondacks that 

 cannot be so classified. In mapping the extension of 

 these doubtful rocks into the Blue Mountain Lake quad- 

 rangle Miller 12 regarded them as mixtures of the Gren- 



10 Cushing, H. P. : N. Y. State Mus., Bull. 95, p. 299, p. 303, 1905. 



11 Cushing, H. P. : N. Y. State Mus., Bull. 115, 1907. 



12 Miller, W. J. : N. Y. State Mus., Bull. 192, 1917. 



