o± Ailing — Problems of Adirondack Precambrian. 



becomes a quartzite ; the garnet and feldspar content con- 

 stituting only a minor portion of the rock. Near Conk- 

 lingville the Hague is highly micaceous. These facts 

 illustrate the variations in the original composition of the 

 clastic deposit. 



One of the most puzzling rocks of the Grenville is the 

 paramphibolite, in that it is frequently a difficult matter 

 to distinguish it from metamorphosed gabbros and dia- 

 bases. The problem of the para- and orthoamphibolites 

 will be discussed on a later page. 



Along the southern shore of Paradox Lake beside the 

 state road a very peculiar rock occurs that was at first 

 sight regarded as a diorite porphyry; a most unexpected 

 rock for the Adirondacks. Investigation eventually 

 showed that it was too soft for an igneous rock and fur- 

 thermore that it grades into a typical crystalline lime- 

 stone. Under the microscope it was found to consist of 

 a very fine-grained groundmass of calcite in which were 

 embedded "phenocrysts" ("pseudocrysts") of augite, 

 orthoclase, quartz and calcite. All of these grains have 

 been recrystallized and secondarily enlarged. It is pos- 

 sible that it represents a limestone conglomerate. 



The Thickness of the Grenville. 



Although the portion of the Grenville studied in detail 

 consists of but a small portion of the whole, the writer 

 cannot regard the original thickness of these ancient sedi- 

 ments to 'have been as great as "W. J. Miller or Adams 

 would have us believe. The evidence that the former 

 presents is based upon the assumption that the Grenville 

 is not isoclinically folded. In view of the fact that iso- 

 clinal folds were found in areas adjacent to those 

 described by Miller, the writer doubts the validity of his 

 conclusion. 



2. The Saranac Series. 



It is customary with some writers in discussing the 

 geology of the Adirondacks to pass in ascending order 

 from a description of the Grenville series directly to the 

 anorthosite-syenite-granite-gabbro series as though there 

 were no rocks of intervening age. The writer suggests 

 that there may be at least four rock groups that are to be 

 classified in this interval. In large measure the relative 

 ages, extent and relationships of these rocks are unknown 



