This is a review of the chronologies based on varved (annually laminated) sediments and a revision of the estimates of the gaps in the varve data. A Finno-Swedish chronology by Gerard De Geer, Ragner Liden, and Matti Sauramo covers the last 11,600 years. It is based on 650 historical years (A.D. 1300-1950), 380 interpolated years (A.D. 920-1300), and the rest on postglacial and glacial varves. The Salpausselka or Younger Dryas age is dated at 10810-10150 B.P. (before the present, 1950). The marked temperature rise which caused the departure of the ice from Salpausselka II in the Finnish year + 1 or 10150 B.P. is taken as the beginning of the Neothermal (European Postglacial) age. The North American chronology ends during the ice oscillations at Cochrane, south of James Bay. These are correlated with the comparably located Nyland and Salpausselka halts in southern Finland. Thus the drainage of Lake Ojibway and varve Timiskaming no. 2025 are dated at about 11300 B.P., and the Cochrane oscillations at 11300-10150 B.P. Then, going backward in time, the Timiskaming retreat occupied 2,025 counted years (varves) plus 525 estimated years (rapid retreat matches the subarctic Allerod age), the Sioux Lookout-Pembroke halt 350 estimated years, the Valders retreat 3,000 counted and 1,800 estimated years, and the St. Johnsbury halt (Valders maximum) 200 counted years. Thus, according to this chronology, the Valders maximum prevailed about 19,200-19,000 years ago. The Mankato culmination at the Altamont moraine occurred slightly later. The estimates of the gaps in the varve records are low, not high. The Valders maximum, marked in the MMwest by the Manistee moraine and correlatives, is recorded in New England by the St. Johnsbury moraine and probably by the Augusta-Belgrade outwash deposits. The preceding relatively warm Two Creeks age matches the rapid Hanover retreat and possibly the Boiling age in Europe. The ice recession from Hackensack in New Jersey to St. Johnsbury, which was interrupted by halts at four separate times, is recorded by 6,830 varves; and, according to one interpretation, three gaps have been estimated at a total of 970 years. Accordingly, the ice border left Hackensack some 27,000 years ago. There are no varve data bearing on the peripheral belt or the terminal moraines. The entire chronology since the uncovering of Hackensack is based on 22,325 varves, 650 historical years, and 4,025 estimated years. However, there was, perhaps, a major interval between the New Haven and the Springfield retreats. If so, the chronology begins with the Springfield retreat and amounts to 23,600 years based on 19,645 varves, 650 historical years, and 3,305 estimated years. The radiocarbon date of 11,400 for the Two Creeks forest bed in Wisconsin cannot be correct. It implies that the Valders-Mankato maximum is some 11,000 years old as against about 19,000 years according to the present chronology. The age of 11,000 years in turn implies that the North American ice sheet still extended into the Great Lakes when the European ice had entirely disappeared, and that the Cochrane oscillations, the subsequent 575-mile retreat to the Labrador ice center, and the time since the ice disappeared together represented less than 3,300 years. The accuracy of radiocarbon dates seems to depend mainly on the history of the materials used. Most erroneous dates seem to be a consequence of change in the proportions of C12 and C14 in the samples by physical contamination with younger organic matter and old carbonates and by decomposition. Most contamination is promoted by ground moisture, but it can take place in absolutely dry caves by visiting burrowing animals. Decomposition, which is performed by microorganisms, mainly aerobic bacteria, requires moisture. When occurring under wet conditions, decay is believed to release relatively fewer C14 atoms than C12 atoms during its early stages, so that the samples give too low dates. However, decomposition upon occasional wetting does not seem to affect the radiocarbon content. The main tasks and problems are to determine which kinds of materials are usable and to find and recognize such materials.