THE ADIRONDACK MOUNTAINS 35 



tliere being a sufficient content of this mineral to warrant its mining, 

 as in Warren and Saratoga counties. 



As will be explained shortly, the Grenville strata are associated 

 with younger rocks of pre-Paleozoic age, these later rocks all being 

 of igneous origin and having cut through the Grenville in hundreds 

 of places and in a most irregular manner, so that the ancient strata 

 are not now present as a single continuous mass of rock occupying 

 the whole Adirondack region. A detailed map of the whole mountain 

 area showing the distribution of the Grenville and later rocks would 

 present a decided " patchwork " effect. Portions only of the region 

 have been thus mapped in detail; the writer's geologic maps of the 

 North Creek, Lake Pleasant and Blue Mountain quadrangles 

 recently published by the New York State Museum afford excellent 

 illustrations of the " patchy " distribution of the Grenville strata. 

 Figure 9 of this volume also suggests the same thing. 



Since the strata of the Adirondacks are usually badly disturbed, 

 tilted and more or less bent or folded, and since neither top nor 

 bottom of the formation has ever been recognized as such, it is 

 impossible to give anything like an exact figure for the thickness 

 of the Grenville rocks. Continuous successions of strata have been 

 observed in enough places, however, to make it certain that the 

 strata were piled, one layer upon another, to a thickness of many 

 thousands of feet. Across a certain valley in Warren county the 

 writer has seen fully 20,000 feet of Grenville strata piled up and 

 only moderately tilted. This clearly implies that the Gren- 

 ville ocean existed for a vast length of time which must be 

 measured by no less than a few million years, because, in the light 

 of all our knowledge regarding the rate of deposition of sediments, 

 such a very long time was necessary for the accumulation of so 

 thick a mass of sedimentary rocks. It does not necessarily follow 

 that the Grenville ocean was thousands of feet deep when the 

 deposition began. In fact, the very character of the sediments 

 clearlv indicates that the Grenville ocean was, for most part at 

 least, of shallow water, for such sediments as sands and muds have 

 rarely if ever been carried far out into an ocean of deep water. 

 The great ocean abysses of today are not receiving any appreciable 

 amount of land-derived sediments. Hence it is practically certain 

 that the very ancient Grenville sea bottom gradually sank as the 

 sediments accumulated. Similar phenomena are definitely known 

 to have occurred in many later basins of deposition. 



There is no evidence whatever for the existence of land life of 

 anv kind during this very early era of earth history. Regarding 



