Since the Archeozoic strata of the Adirondack Mountains, southeastern Canada, and also all, or nearly all, other known districts are mostly badly disturbed, tilted, and more or less bent or folded, and since neither top nor bottom of the piles of strata has ever been recognized as such, it is impossible to give anything like an exact figure for the thickness of the series. Continuous successions of strata have, however, been observed in enough places to show that they were commonly deposited layer upon layer to a thickness of at least some tens of thousands of feet. A thickness of over 100,000 feet has been reported from southeastern Canada. The clear implication is that the Archeozoic sea which received sediments must have existed for a vast length of time which must be measured by at least some millions of years, because in the light of all our knowledge regarding the rate of accumulation of sediments a very long time was necessary for the piling up of such thick masses of strata. It does not, however, necessarily follow that the Grenville ocean was many thousands of feet deep where deposition took place. In fact, the very character of the original sediments (muds, sands, and limes) clearly indicates that the Archeozoic sea in which they accumulated was, for most part at least, of shallow water because such sediments have rarely, if ever, been carried out into an ocean of deep water. The great ocean abysses of to-day are not receiving any appreciable amount of land-derived sediment. Thus we are forced to conclude that in Archeozoic time, as well as many times in later ages, the shallow sea bottom gradually sank while the sediments accumulated. Even more conclusive proof of such subsidence has been obtained from the study of so-called "folded" mountain ranges of Paleozoic and later time, an excellent example being the Appalachian Range. Having established the sedimentary origin and great antiquity of the Grenville series, we are led to the interesting and important conclusion that these oldest known rocks are not the most ancient which ever existed, because the Grenville strata must have been deposited layer upon layer, upon a floor of still older rocks. If such still older rocks are anywhere exposed to view, they have never been recognized as such. Again, the fact that the most ancient known rocks were deposited under water carries with it the corollary that there must have been lands at no great distances from the areas of deposition because, then as now, such sediments as muds and sands could have been derived only from the wear or erosion of lands, and have been deposited in layers under water adjacent to those lands. But we are utterly in the dark regarding any knowledge of the location or character of such very ancient lands.