Early Pleistocene Glaciation Research Articles

Early Pleistocene volcanism and glaciation in central Yukon: a new chronology from field studies and paleomagnetism

The paleomagnetism of the Selkirk Volcanics and nearby stratified Pleistocene sediments was investigated to resolve the chronology of Early Pleistocene glaciations in central Yukon. Radiometric dates on these low-K basalts have proven to be erroneously old. Most sampled sediments and all basalts accurately record the paleofield and true reversals. The valley-filling phase of the Selkirk Volcanics was in part coeval with the younger pre-Reid glaciation. It was erupted during the Matuyama Chron, either post-Cobb Mountain Subchron or post-Jaramillo Subchron, over a period too brief to average secular variation. The older pre-Reid glaciation occurred after ca. 1.60 Ma and prior to the eruption of the Fort Selkirk tephra (pre-Jaramillo or pre-Cobb Mountain). Sediments investigated at Revenue Creek and Braden's Canyon are normally magnetized. The assigned Brunhes age is compatible with their occurrence in valleys that were cut or deepened sometime after the pre-Reid glaciations.

Late Wisconsin glaciation of Tasmania

During the Late Wisconsin, icecap and outlet glacier systems developed on the West Coast Range and on the Central Plateau of Tasmania. Local cirque and valley glaciers occurred in many other mountain areas of southwestern Tasmania. Criteria are outlined that enable Late Wisconsin and older glacial landforms and deposits to be distinguished. Radiocarbon dates show Late Wisconsin ice developed after 26-25 ka BP, attained its maximum extent c. 19 ka BP, and disappeared from the highest cirques before 10 ka BP. Important Late Wisconsin age glacial landforms and deposits of the West Coast Range, north-central and south-central Tasmania are described. Late Wisconsin ice was less extensive than ice formed during middle and earlier Pleistocene glaciations. Late Wisconsin snowline altitudes, glaciological conditions and palaeoclimatic conditions are outlined.

Zur Problematik der pleistozänen und holozänen Vergletschernung Süd-Kamtschatkas – erste Ergebnisse bodengeographischer Untersuchungen

Abstract. In the Plotnikova Valley, west of Petropavlovsk in South Kamchatka, two valley drift complexes can be identified. They are correlated with glaciofluvial terraces. The older, so called M1-moraines descend to about 300 m a.s.l. corresponding with the T1-terraces; they are smoothand vague-shaped, without kettles. The younger, so called M2-moraines descend to 350-450 m a.s.l.; their relief is well formed and rich in kettles and ridges, and they are connected with the T2-terraces. The soils developed on these drifts and terraces do not differ significantly with respect to colour and weathering intensity. Soils of the older drift and terraces reveal stronger cryogenetic disturbances and their boulders and gravels are characterized by more pronounced weathering crusts in comparison to the younger drift and terraces. No features indicating interglacial weathering can be identified in the subsoils. But all soils are stratified by 3-4 tephra layers, due to the following eruptions: tephra 1 = Opala, 1400-1500 a BP; tephra 2 = Ksudach 1, 1700-1800 a BP; tephra 3 = Ksudach 2 = 6000 a BP; tephra 4 = Kuril Lake Il'inskay, 7600-7700 a BP (BRAITSEVA et al. 1992). According to these results it is supposed that both moraines indicate Late Pleistocene glaciation; the M1 drift was deposited during an early phase of the Late Pleistocene, the M2 drift characterizes a second phase of the Late Pleistocene, separated only by an interstadial, not by an interglacial. In contrast to Middle Europe, early Late Pleistocene glaciation has been more pronounced than Late Pleistocene second phase glaciation. Studying soil development on frontal moraines along a sequence from 350 to 1000 m a.s.l. in the Topolovaya-Valley it was found that up to about 930 m a.s.l. all soils are stratified by tephra 1-4 layers, indicating that the age of the corresponding moraines is older than 7600/7700 a BP. Drift in about 980 m a.s.l. shows only tephra 1 and 2. These moraines are older than 1700/1800 a BP, but younger than 6000 a BP. Probably they indicate a glacial advance during the middle Holocene (Neoglacial). In 1000 m a.s.l. two additional ridges can be identified, well formed with initial soil formation but without tephra. According to the lichenometric results they characterize snow and ice accumulations during the so-called "Little Ice Age".

A record of Early Pleistocene glaciation on the Mount Edziza Plateau, northwestern British Columbia

Mount Edziza is a Plio-Pleistocene volcanic complex that is located in the Stikine Terrane in northwestern British Columbia. A sequence of diamictites preserved between Ice Peak Formation basalts on the northwestern blank of Mount Edziza records an Early Pleistocene regional glaciation. The lowest Ice Peak Formation basalt flow (IP1; about 1 Ma) was probably extruded onto glacial ice because it is deformed and brecciated, it is pillowed at the base, it lies directly on hyaloclastite deposits, and there is a lack of fluvial and lacustrine sediments at the base. Fabric measurements from the underlying diamictites are consistent with lodgement processes and indicate northwest and southwest transport directions. These data, and an abundance of striated exotic cobbles, indicate that the sediment was deposited by Coast Mountain ice. Radiometric, paleomagnetic, and stratigraphic data all support the interpretation that diamictites at the section are the sedimentary record of an Early Pleistocene (about 1.1 Ma, isotope stage 32–34) regional glaciation(s). The normal paleomagnetic polarity of one of the Ice Peak Formation basalts (IP2) records extrusion during the Jaramillo normal polarity subchron (1.07–0.99 Ma) and further constrains the age of the underlying diamictites.

Paleomagnetism of tills and associated paleosols in southwestern Alberta and northern Montana: evidence for Late Pliocene–Early Pleistocene glaciations

Sequences of pre-Wisconsinan till and intercalated paleosols were sampled for paleomagnetic study. The tills were deposited during successive glaciations and the paleosols formed during interglacial intervals. Paleoargillic horizons of the paleosols and the carbonate cement (calcrete) found in some till–paleosol units generally yielded excellent data. Magnetizations of paleosols probably were acquired during the formation of the paleosols rather than during initial deposition of the tills in which they were developed. At Mokowan Butte (Alberta), the lowest paleosol has normal polarity, two of the middle tills have reversed polarity, and the uppermost till–paleosol unit has normal polarity. At Saint Mary Ridge (Montana), three of the lower tills have reversed polarity, and the upper two till–paleosol units have normal polarity. At Two Medicine Ridge (Montana), the lowest three tills are reversed, but the paleoargillic horizon on the uppermost (fourth) till is normal. Magnetostratigraphic correlation indicates that at least six glacial and six interglacial episodes are represented in the Kennedy Drift. The upper normal polarity units are interpreted as having been developed during the Brunhes Normal Chron, the underlying reversed polarity sediments during the Matuyama Reversed Chron, and the lowest normal polarity unit at Mokowan Butte during the Gauss Normal Chron. The oldest glaciations here extend into the Pliocene (2600 ka), making these sediments among the oldest glacial deposits in North America. Alternatively, the lowest normally magnetized paleosol at Mokowan Butte may have formed during either the Jaramillo or the Olduvai subchrons, although this is considered less likely.

Late Cenozoic surficial deposits and valley evolution of unglaciated northern New Jersey

Multiple alluvial, colluvial, and eolian deposits in unglaciated northern New Jersey, and the eroded bedrock surfaces on which they rest, provide evidence of both long-term valley evolution driven by sustained eustatic baselevel lowering and short-term filling and excavation of valleys during glacial and interglacial climate cycles. The long-term changes occur over durations of 10 6 years, the short-term features evolve over durations of 10 4 to 10 5 years. Direct glacial effects, including blockage of valleys by glacial ice and sediment, and valley gradient reversals induced by crustal depression, are relatively sudden changes that account for several major Pleistocene drainage shifts. After deposition of the Beacon Hill fluvial gravel in the Late Miocene, lowering of sea level, perhaps in response to growth of the Antarctic ice sheet, led to almost complete dissection of the gravel. A suite of alluvial, colluvial, and eolian sediments was deposited in the dissected landscape. The fluvial Bridgeton Formation was deposited in the Raritan lowland, in the Amboy-Trenton lowland, and in the Delaware valley. Following southeastward diversion of the main Bridgeton river, perhaps during Late Pliocene or Early Pleistocene glaciation, northeastward drainage was established on the inactive Bridgeton fluvial plain. About 30 to 45 m of entrenchment followed, forming narrow, incised valleys within which Late Pleistocene deposits rest. This entrenchment may have occurred in response to lowered sea level caused by growth of ice sheets in the northern hemisphere. Under periglacial conditions in the Middle and Late Pleistocene, valleys were partially filled with alluvium and colluvium. During interglacials slopes were stabilized by vegetation and the alluvial and colluvial valley-fill was excavated by gullying, bank erosion, and spring sapping. During Illinoian and late Wisconsinan glaciation, the lower Raritan River was diverted when glacial deposits blocked its valley, and the Delaware River was partially diverted down the isostatically-steepened lower Millstone valley.

Sedimentology and depositional model for glaciolacustrine deposits in an ice‐dammed tributary valley, western Tasmania, Australia

ABSTRACTQuaternary sedimentary successions are described from the Linda Valley, a small valley in western Tasmania that was dammed by ice during Early and Middle Pleistocene glaciations. Mapping and logging of exposures suggest that an orderly sequence of deposits formed during ice incursion, occupation and withdrawal from tributary valleys. Four principal sediment assemblages record different stages of ice occupation in the valley. As the glacier advanced, a proglacial, lacustrine sediment assemblage dominated by laminated silts and muds deposited from suspension accumulated in front of the glacier. A subglacial sediment assemblage consisting of deformed lacustrine deposits and lodgement till records the overriding of lake‐bottom sediments as the glacier advanced up the valley into the proglacial lake. As the glacier withdrew from the valley, a supraglacial sediment assemblage of diamict, gravel, sand and silt facies formed on melting ice in the upper part of the valley. A lacustrine regression in the supraglacial assemblage is inferred on the basis of a change from deposits mainly resulting from suspension in a subaqueous setting to relatively thin and laterally discontinuous laminated sediments, occurrence of clastic dykes, and increasing complexity of the geometry of deposits that indicate deposition in a subaerial setting. A deltaic sediment assemblage deposited during the final stage of ice withdrawal from the valley consists of steeply dipping diamict and normally graded gravel facies formed on delta foresets by subaqueous sediment gravity flows. The sediment source for the delta, which prograded toward the retreating ice margin, was the supraglacial sediment assemblage previously deposited in the upper part of the valley. A depositional model developed from the study of the Linda Valley may be applicable to other alpine glaciated areas where glaciers flowed through or terminated in medium‐ to high‐relief topography.

A record of Pliocene and Pleistocene glaciations and climatic changes in the North Atlantic based on variations in volcanic and sedimentary facies in Iceland

The location of Iceland directly below the Arctic Circle and on the North Atlantic plate boundary gives the island a characteristic record of interbedded lavas, glacial deposits and other sediments, opening a window on the geological and climatic history of the North Atlantic. Frequently extruded lava flows tend to shield underlying sediments from subsequent erosion. Explosive volcanism keeps the sedimentation rate high and produces extensive time markers. Continuing studies of diamictites interbedded within basaltic lava suites of Cainozoic age in Iceland deal specifically with the problem of differentiating between glacial and non-glacial sediments that have very similar attributes. A multifaceted approach has been taken in order to differentiate these deposits. This includes both lateral and vertical lithofacies description and clast fabric studies based on extensive field work, a comparison with modern analogues, and detailed laboratory work (textural studies on thin sections and palaeomagnetic studies). The results suggest that both the nature and extent of late Pliocene and early Pleistocene glaciations can be inferred from the preserved record. The rock sequence offers excellent opportunities for pinning down the age of each event through palaeomagnetic correlation and radiometric dating of the lava flows. The oldest tillite along the north coast of Iceland has been bracketed down to approximately 2.1 Ma, and in inland mid-western Iceland to approximately 2.6 Ma. It is anticipated that continuing work elsewhere in Iceland can further define the trends of Pliocene glaciation in the North Atlantic. The significance of the frequency of identified glacial deposits in the Icelandic sections may be tested through comparison with the latest deep-sea record of glacial-interglacial cycles.

Evolution and zoogeography of the invertebrate cave faunas of the Driftless Area of the Upper Mississippi River Valley of Iowa, Minnesota, Wisconsin, and Illinois, U.S.A.

This paper reports the results of a long-term survey of the invertebrates living in caves and other subterranean habitats in the Upper Mississippi River Valley, particularly in the region frequently but erroneously called the Driftless Area. Sixteen troglobitic species are known: two flatworms, two amphipods, one isopod, four spiders, one mite, and six collembolans. The terrestrial troglobite fauna probably represents cave invasion and isolation following Early Pleistocene glaciation, and demonstrates that the caves were habitable while the region was at the margin of Late Pleistocene glaciations. The groundwater troglobite fauna may have survived in situ while the region was covered by glacial ice in the Early Pleistocene. The troglophile fauna consists of at least 78 species, and these species may or may not have come into the region since the Wisconsinan glaciation recession. The presence of troglophile species in a particular cave is highly sporadic.

Stratigraphy and magnetic polarity of the high terrace remnants in the upper Ohio and Monongahela Rivers in West Virginia, Pennsylvania, and Ohio

A synthesis of previous work and new data on the stratigraphy of high terraces of the Ohio and Monongahela Rivers upstream from Parkersburg, West Virginia, indicates a correspondence between terrace histories in the ancient Teays and Pittsburgh drainage basins. Four terraces are identified in each. Sediments of the lower three alluvial and slackwater terraces, correlated with Illinoian, early Wisconsin, and late Wisconsin glacial deposits, have been traced along the modern Ohio River through the former divide between the Teays and Pittsburgh basins. Sediments in the fourth terrace, the highest well-defined terrace in each basin, were deposited in two ice-dammed lakes, separated by a divide near New Martinsville, West Virginia. Some deposits of the highest slackwater terrace in both the Teays and Pittsburgh basins have reversed remanent magnetic polarity. This, and the stratigraphic succession in the two basins, suggests that both were ponded during the same glaciation. Reversed polarity in these terrace sediments restricts the age of the first ice-damming event for which stratigraphic evidence is well-preserved to a pre-Illinoian, early Pleistocene glaciation prior to 788,000 yr ago. In contrast, slackwater sediments in the Monongahela River valley, upstream from an outwash gravel dam at the Allegheny-Monongahela confluence, have normal remanent magnetic polarity, corroborating correlation with an Illinoian ponding event.

Glaciation in New Zealand — the first century of research

The year 1965 is seen as the end of a prolonged pioneering stage in New Zealand Quaternary studies. Description of evidence of formerly extended glaciers began in 1861, and by 1965 about 138 relevant publications had appeared. The following factors and developments in particular influenced directions and progress: (1) initially, ongoing 19th century interest in the ‘Glacial Controversy’ and consequently in ‘Ice Age’ manifestations in the large, isolated, middle-latitude islands of New Zealand; (2) from 1864, vigorous gold-mining excavations in Quaternary morainic deposits; (3) throughout the period, domestic disputes about the extent of glacierisation, the number and dates of glacial events; (4) especially after 1917, consistent extension of sound stratigraphic terminology throughout New Zealand; (5) in 1944, recognition of evidence for temperature fluctuations in fossiliferous Late Tertiary/Pleistocene marine strata in North Island, with prospects for correlation with South Island glacial events; (6) after World War II, more overseas contacts and experience, giving confidence to those developing independent criteria for distinguishing and evaluating successive ice advances and non-glacial interludes; (7) also mainly since the War, facilities for aerial mapping, radiocarbon dating and palynology; (8) a new 1:250,000-scale mapping programme by the Geological Survey begun in 1957, which raised many nomenclatural questions. From 1957, internal glacial correlations and progress towards an essentially climate-stratigraphic classification culminated in Suggate's 1965 scheme, embodying a Holocene subdivision preceded by four Late Pleistocene glacial stages with non-glacial interludes and by an Early Pleistocene glaciation. Despite some correlation problems and questions as to the status of certain intervals, the scheme has been widely accepted and used. Recent work, however, suggests that the time for substantial revision is at hand.

The New Zealand Scincidae (Reptilia: Lacertilia); a taxonomic and zoogeographic study

This revision of the New Zealand Scincidae recognises 22 species, in the genera Leiolopisma Duméril & Bibron and Cyclodina Girard. The following species are redescribed: L.fallai McCann; L. suteri (Boulenger); L. smithi (Gray); L. homalonotum (Boulenger); L. moco (Duméril & Bibron); L. infra‐punctatum (Boulenger); L. striatum (Buller); L. zelandicum (Gray); L. nigriplantare (Peters); L. lineoocellatum (Duméril & Duméril); L. grande (Gray); L. otagense McCann; L.(?) fasciolare (Girard); C. ornata (Gray); C. aenea Girard; C. oliveri (McCann); C. alani (Robb); and C. macgregori (Robb). L.(?) fasciolare is included in Leiolopisma only provisionally pending further examination; doubts regarding its inclusion in the New Zealand herpetofauna are raised. Leiolopisma gracilicorpus, L. chloronoton, L. acrinasum, and Cyclodina whitakeri are erected as new species. Only 2 subspecies are recognised, in L. nigriplantare. L. n. nigriplantare includes animals described earlier as L. dendyi (Boulenger) and L. turbotti McCann, and L. n. maccanni includes those animals referred to under the name L. zelandica by McCann (1955). Two forms of L. otagense are recognised, but are not accorded subspecific status. L. pachysomaticum Robb, 1975 is reduced to synonymy with Cyclodina oliveri. Hinulia variegata Buller is declared a nomen dubium. Electrophoretic studies of lactate dehydrogenase (LDH) isozymes and haem compounds appear to confirm the species recognised on morphological characteristics. Analyses of LDH isozymes suggest close phylogenetic relationships within 3 groups of species: Leiolopisma striatum and L. zelandicum; Cyclodina ornata and C. aenea; and C. oliveri, C. alani, and C. whitakeri. Investigations into the relative evolutionary stability of haemoglobins and morphological characters indicate that rates of evolution may differ, both within and between species. Evidence is presented to show that the evolution of haemoglobins cannot necessarily be taken to have occurred at similar rates overall in the New Zealand skink species. It is suggested that Cyclodina arose from a pre‐Leiolopisma stock before the development of the palpebral disc characteristic of Leiolopisma. The genus Leiolopisma is thought to have arisen in a region north of Australia, and to have given rise in that area to 2 early offshoots, the first represented today by L. spenceri and L. palfreymani and the second by L. telfairi and L. lichenigera. Subsequent dispersal of the genus is believed to have been via the New Caledonian region, where further divergence resulted in forms now present in Australia (L. coventryi and L. entrecasteauxi) and New Zealand (the entire Leiolopisma fauna). The New Zealand Leiolopisma species are all endemic at the specific level, and are likely to represent late Pliocene invasions. The Australian Leiolopisma species characterised by fused frontoparietals are considered to represent a second invasion of that continent from the New Caledonian region. Cyclodina probably reached New Zealand via the New Caledonian region, at latest by the early Pleistocene. The genus has not been recorded from outside New Zealand (although revision of the generic placement of L. euryotis, from New Caledonia, is necessary owing to its strong affinities with Cyclodina). Uncertainty as to the effects of early Pleistocene glaciations on the distribution and isolation of the New Zealand species inhibits discussion of their zoogeography. Nevertheless, 3 geographic groups of species are recognised in the New Zealand Leiolopisma fauna. The northernmost is believed to have arisen from invaders from the New Caledonian region; the central and southern groups from an easterly movement of invaders from Australia. L. suteri probably represents yet another invasion. The present distribution of species indicates that the following refuges persisted in the South Island during the last Pleistocene glaciation: coastal Fiordland; Southland and Stewart Island; Otago and Banks Peninsulas; and the Nelson/Marlborough Sounds region. Isolation of populations in the vicinity of the Otago and Banks Peninsulas has probably been important in the divergence of 2 forms within L. otagense. Haem banding patterns suggest that relict populations of L. nigriplantare exist at Te Anau and on Stewart Island, and a post‐Pleistocene reinvasion of the central South Island by that species is indicated. Subspeciation of L. nigriplantare on the Chatham Islands is also thought to have occurred after the Pleistocene.

Stadial subdivisions of early Pleistocene glaciations in central United States ‐ a developing chronology

Recently recognized field evidence clearly indicates that both the Nebraskan and Kansan Glaciations are divisible into stades on the basis of a stratigraphic record of ice‐margin fluctuations. Two Nebraskan stades and three Kansan stades have been identified; it is suggested that others will be found. Recognition of multiple stades requires a thorough review of all Early Pleistocene stratigraphic and paleontologic age assignments applied in the American Midwest.

Evidence of Multiple Stades in the Lower Pleistocene of Northeastern Kansas

Nebraskan and Kansan glacial and glacio-fluvial deposits in Kansas occur only in the northeastern part of Kansas. generalized four-fold history of continental glaciation has long been accepted in the United States. Generally the highest till was correlated with the youngest glaciation and an underlying till correlated with the next youngest glaciation. In areas where only early Pleistocene glaciations occurred, this same method of correlation was practiced. Recognition of a more complex system of advances and retreats of ice in the Wisconsinan Stage lead to the adoption of substage or stade division of this stage. Each of the glacial stages is separated from the succeeding glacial stage by an interglacial stage. This period was one of relative stability under comparatively warm conditions during which extensive interglacial soils were developed in the periglacial regions as well as in the glaciated regions. Buried profiles of weathering, or fossil soils, are perhaps the most usable criteria for stratigraphic correlation and classification of the Pleistocene sediments in Kansas. The top of a buried soil is unmistakably an unconformity, and where deep well-developed soil profiles occur, a significant interval of nondeposition and only slight erosion is indicated. Interpretation of the soils within the Pleistocene sequence involves the evaluation of the soil horizons as interglacial or interstadial and may lead to errors in correlation. The strength of soil development is believed to be the most important factor in this interpretation. Pronounced zones of clay enrichment in the B horizon, considerable depth of leaching, great depth of oxidation, and significant thicknesses of secondary lime accumulation are believed to be more important and better indicators of interglacial nature of soils than the thickness of the humic A horizon which often has been removed by erosion or scour. Frye and Leonard (1949, 1952) described the exposure of two tills in a quarry in the Missouri River Bluff near Iowa Point in northeastern Doniphan County. well-developed soil on the lower till was indicative of a long period of weathering prior to deposition of the upper till.

Calcutta Silt,a Very Early Pleistocene Deposit, Upper Ohio Valley

Unconsolidated,laminated,weathered, silty material,called the Calcutta Silt in this report, and soils formed in it occur near Calcutta and Wellsville,Columbiana County,Ohio. The silt mantles most of the land surface on benches at elevations of 1080-1180 feet in the unglaciated Allegheny Plateau;it is also buried beneath the gravelly outwash of very early Pleistocene glaciation on a terrace at 970 feet,which is part of the Teays-age level in the region.It does not extend over nearby higher slopes and ridgetops of 1200 feet and higher. The Calcutta Silt,apparently a water-laid deposit,is 2-10 feet thick and contains thin sandy layers and pebbles from local sedimentary rocks. Cobbles and pebbles of very resistant crystalline rocks occur at places on the surface. The Calcutta Silt is a remnant of a former lake bed created during very early Pleistocene glacial ponding of the preglacial northward-draining Old Monongahela System.

Pleistocene glaciation in the Trinity Alps of northern California

The glacial sequence of the Trinity Alps has good development, significant location, and value as a reference datum for other Pleistocene events. The principal glacial episodes identified are Late (Morris Meadow), Middle (Rush Creek), Early (Alpine Lake) and Ancient (Swift Creek). The 3 youngest are judged Wisconsin, the oldest pre-Wisconsin. Other evidence suggests possibly still older glaciations, and youthful moraines at high elevations may be Neoglacial (post-Hypsithermal). During the Late (morris Meadow) glaciation, the Trinity Alps contained at least 30 valley glaciers. Maximum lengths and lowest elevations attained are: Late, 7.8 mi. and 3,350 ft.; Middle, 9.3 mi. and 2,800 ft.; Early, 11.3 mi. and 2,500 ft.; Ancient, 13.7 mi. and 2,450 ft. Length was more variable than terminal elevation. Where the glacial detritus was derived largely from serpentine, numerous debris flows extended down-valley from glacier snouts. Deposits of flow debris, almost indistinguishable from till, complicate interpretation of glacial relations on lower Deer and Swift creeks. The rock floors of stream terraces, well exposed in abandoned placer workings along Canyon Creek, lie at 10, 20, 40, 90, 160, and 300 ft. above the stream. Direct tracing to terminal-moraine positions suggests that the 10-, 20-, and 40-ft, rock-terrace levels are chronologically, but perhaps not genetically, related to the Late, Middle, and Early phases of Wisconsin glaciation. The 90-ft. terrace may be a time-equivalent of the Ancient glaciation (pre-Wisconsin), and the 160- and 300-ft. terrace could be chronologically related to still earlier Pleistocene glaciations. In the high country, carapaces of ice formed on sloping valley walls above the level of the ice streams partly filling the valleys. Two vestigial glacierets remain at elevations of 8,200-8,400 ft. on the N. side of the Thompson Peak ridge. Wisconsin orographic snowline lay at 6,500 ft., climatic snowline at about 8,000 ft. Corresponding figures for the present are judged to be about 7,500 and 9,000 ft. Wisconsin orographic snowline rose inland 18 ft. per mi., judging from data obtained on Mt. Lassen, 85 mi. to the ESE.

Anomalous glacial deposits in the Colorado Front Range area, Colorado

Reinvestigation of reported glacial deposits in the Colorado Front Range area, in locations above or exterior to those commonly classed as glaciated, has resulted in a doubling of the number of known deposits, and the finding of a rough gradation from glacial, near the Arapaho Massif; through reworked glacial, at distances of six or seven miles; to glacio‐fluviatile and fluviatile at greater distances. From this evidence, one or more early Pleistocene glaciations are postulated, the parent ice body being of the ice‐cap type, resting upon a gently rolling terrain of which only the so‐called peneplain surfaces now remain. A similar large ice cap in the Laramie‐Poudre area is suggested by scattered evidence between those river s and the Laramie‐Fort Collins highway.

The Bearing of Some Remarkable Potholes on the Early Pleistocene Glaciation of the Front Range, Colorado

The eastern flank of the Front Range in north central Colorado shows a remarkable series of potholes related to the early Pleistocene glaciation of the region. The areas concerned are deeply and thickly pitted with thousands of glacially carved potholes. The bearing of these ancient potholes on the condition of the ice during their formation indicates unusual features of crevassing and surface ablation. The potholes are directly linked up with ancient cirques, U-shaped valleys, striae, and perched bowlders in the chain of evidence which indicates that these early Pleistocene glaciers covered 75 to 80 per cent of the region and had many of the characteristics of an ice cap with pendant valley glaciers, fringing well out to the foothills.