Mosquito Range Research Articles

Nutritional Stress Affects Mosquito Survival and Vector Competence for West Nile Virus

Most anautogenous female mosquitoes ingest plant carbohydrates for flight energy and survival, and they imbibe vertebrate blood for egg development. We evaluated the effect of different sucrose meals following a blood meal containing West Nile virus (WNV) on Culex pipiens pipiens survival, nutritional status, and susceptibility to viral infection and transmission. Ten days after blood feeding, no mosquitoes survived on distilled water, 55% survived on 2% sucrose, 61% on 10 and 20% sucrose meals, and over 70% survived on 40% sucrose. There was a positive correlation between sucrose meal concentration and detectable sugars, glycogen, and lipid in whole-body homogenates. Average sugar values increased from 0 microg per starved mosquito (range 0-1.0 microg) to an average of 392 microg per mosquito fed on 40% sucrose (85-1088 microg). Average glycogen values increased from 0 microg (0-5.7 microg) to an average of 620 microg (118-1421 microg). Average lipid values were identical for mosquitoes in the starved and 2% sucrose series (38 microg) and increased to 172 microg per mosquito fed on 40% sucrose (92-266 microg). Mosquitoes in all sucrose series were equally susceptible to WNV infection (p > 0.5), but mosquitoes with lower nutrient reserves as a result of lower sucrose meals were more likely to orally transmit virus (p < 0.05). We discuss how mosquito nutritional status influences probability of daily survival, susceptibility to infection, and vectorial capacity. We conclude that maintaining C. p. pipiens on standard 10% sucrose is justified in light of these results.

Effects of Expanded Mosquito Range

The aggressive spread of Aedes albopictus as it has leapfrogged across geographic boundaries was well documented by M. Enserink in his News Focus story, “A mosquito goes global” (16 May, p. [864][1]). The impact of Ae. albopictus on vector-borne disease transmission dynamics remains unresolved;

Satellite-Based Modeling of Anopheles Mosquito Densities on Heterogeneous Land Cover in Western Thailand

Landsat 5 TM was used as a tool to model Anopheles mosquito densities on heterogeneous land cover. In this study, mosquito density data was divided into five classes; absence, low, moderate, high, and very high densities. Land cover was classified into eight types. Stagnant water, wetland, and paddy land cover types are larva habitat. Forest, cropland, orchard, and grassland land cover types are adult habitat. Built-up land is non habitat. Multiple linear regression and discriminant analysis were selected to identify the relationship between mosquito densities and land cover types. For the average flight range of mosquitoes, 1000, 2000, and 3000 meters buffer were used as the sample zones around the collected points to test the relationship between them. The results revealed that discriminant analysis is the best statistical model for fitting the model. The mosquito flight range of 1000, 2000, and 3000 meters were predicted with accuracies up to 80%, followed by 74.3%, and 54.3%, respectively. Relationships between mosquito density and heterogeneous land cover in this study appear to be varied upon forest, grassland, and larva habitat within the 1000 meters buffer, likewise, forest, and larva habitat within 2000 meters buffer.

Gore′s Fever and Dante′s Inferno: Chikungunya Reaches Ravenna

Gore′s Fever and Dante′s <i>Inferno:</i> Chikungunya Reaches Ravenna

Different retina-lamina projections in mosquitoes with fused and open rhabdoms

Anopheles gambiae and Toxorhynchites brevipalpis represent the nocturnal and diurnal extremes of the mosquito light intensity range, and their eyes are structurally very different. A. gambiae has fused rhabdoms with huge acceptance angles, whereas T. brevipalpis has open rhabdoms with rhabdomere acceptance angles comparable with those of advanced (brachyceran) flies. Here, we show that the retina-lamina projections are consistent with these differences. The short receptor axons from each ommatidium in A. gambiae insert as a group between four lamina monopolar cell clusters. In T. brevipalpis axon bundles from each ommatidium undergo a twist in their passage through the nuclear layer of the lamina, and then fan out into a space the diameter of which is about twice the separation of the monopolar cell clusters. This arrangement is consistent with a neural superposition mechanism closely similar to that found in higher Diptera, but which must have evolved independently.

Venezuelan equine encephalitis.

Venezuelan equine encephalitis virus (VEEV) remains a naturally emerging disease threat as well as a highly developed biological weapon. Recently, progress has been made in understanding the complex ecological and viral genetic mechanisms that coincide in time and space to generate outbreaks. Enzootic, equine avirulent, serotype ID VEEV strains appear to alter their serotype to IAB or IC, and their vertebrate and mosquito host range, to mediate repeated VEE emergence via mutations in the E2 envelope glycoprotein that represent convergent evolution. Adaptation to equines results in highly efficient amplification, which results in human disease. Although epizootic VEEV strains are opportunistic in their use of mosquito vectors, the most widespread outbreaks appear to involve specific adaptation to Ochlerotatus taeniorhynchus, the most common vector in many coastal areas. In contrast, enzootic VEEV strains are highly specialized and appear to utilize vectors exclusively in the Spissipes section of the Culex (Melanoconion) subgenus.

Mining among the Clouds: The Mosquito Range and the Origins of Colorado's Silver Boom Harvey N. Gardiner

Mining among the Clouds: The Mosquito Range and the Origins of Colorado's Silver Boom Harvey N. Gardiner

Fallen arches: Dispelling myths concerning Cambrian and Ordovician paleogeography of the Rocky Mountain region

High-resolution sedimentologic, biostratigraphic, and stable isotope data from numerous measured sections across Colorado reveal a complex architecture for lower Paleozoic strata in the central Cordilleran region. A lack of precise age control in previous studies had resulted in misidentification and miscorrelation of units between separate ranges. Corrections of these errors made possible by our improved data set indicate the following depositional history. The quartz-rich sandstone of the Sawatch Formation was deposited during onlap of the Precambrian erosion surface in the early Late Cambrian. The overlying Dotsero Formation, a regionally extensive carbonate- and shale-rich succession records blanket-like deposition with only minor facies changes across the state. An extremely widespread, meter-scale stromatolite bed, the Clinetop Bed, caps the Dotsero Formation in most areas. However, a latest Cambrian erosional episode removed 9–11 m of the upper Dotsero Formation, including the Clinetop Bed, from just east of the Homestake shear zone in the Sawatch Range eastward to the Mosquito Range. The overlying Manitou Formation differs in character, and thus in member stratigraphy, on the east vs. west sides of the state. These differences were previously interpreted as the result of deposition on either side of a basement high that existed within the Central Colorado Embayment or Colorado “Sag,” a region of major breaching across the Transcontinental Arch. This paleogeographic reconstruction is shown herein to be an artifact of miscorrelation. Biostratigraphic data show that the northwestern members of the Manitou Formation are older than the members exposed in the southeastern part of the state and that there is little or no overlap in age between the two areas. This circumstance is the result of (1) removal of older Manitou Formation strata in the southeast by an unconformity developed during the Rossodus manitouensis conodont Zone, and (2) erosion of younger Manitou strata in central and western Colorado along Middle Ordovician and Devonian unconformities. Deciphering these complex stratal geometries has led to invalidation of long-held views on western Laurentian paleogeography during the Cambrian and earliest Ordovician, specifically the existence of the Colorado Sag and a northeast-trending high within the sag that controlled depositional patterns on either side. The mid- Rossodus uplift and resultant unconformity eliminated any and all Upper Cambrian and Lower Ordovician deposits in southern Colorado and northern New Mexico, and thus their absence should not be misconstrued as evidence for earlier nondeposition in this region. Lithofacies distribution patterns and isopach maps provide no evidence that highlands of the Transcontinental Arch existed in Colorado prior to the mid- Rossodus age uplift event. In fact, regional reconstructions of earliest Paleozoic paleogeography along the entire length of the purported Transcontinental Arch should be reevaluated with similarly precise biostratigraphic data to reconsider all potential causes for missing strata and to eliminate topographic elements not supported by multiple stratigraphic techniques. This study illustrates how seriously paleogeographic reconstructions can be biased by the presumption that missing strata represent periods of nondeposition rather than subsequent episodes of erosion, particularly in thin cratonic successions where stratigraphic gaps are common and often inconspicuous.

Soil Relative Dating of Moraine and Outwash-terrace Sequences in the Northern Part of the Upper Arkansas Valley, Central Colorado, U.S.A.

Profile development indices for soils developed in moraines and outwash near Twin Lakes and in outwash near Leadville support the correlation of moraines with subdued morphology and two high outwash terraces with the Bull Lake glaciation (ca. 130–160 ka) and the correlation of hummocky moraines and two low outwash terraces with the Pinedale glaciation (ca. 14–47 ka). Elsewhere in the northern part of the upper Arkansas Valley, glacial sequences are correlated by mapping outwash terraces near the mouths of major tributaries of the Arkansas River. Near Twin Lakes, indices for soils on low, outer lateral moraines suggest that the older Pinedale glaciers extended beyond the margin of high, younger Pinedale lateral moraines with hummocky topography. A few subdued moraines near Twin Lakes and Leadville probably record one or more glaciations significantly older than the Bull Lake. The downvalley extent of Pinedale glaciers in the Mosquito Range on the east side of the Arkansas Valley is uncertain: most likely, Pinedale glaciers were almost as extensive as Bull Lake glaciers but built no prominent terminal moraines at their maximum positions.

Soil Relative Dating of Moraine and Outwash-Terrace Sequences in the Northern Part of the Upper Arkansas Valley, Central Colorado, U.S.A.

Profile development indices for soils developed in moraines and outwash near Twin Lakes and in outwash near Leadville support the correlation of moraines with subdued morphology and two high outwash terraces with the Bull Lake glaciation (ca. 130-160 ka) and the correlation of hummocky moraines and two low outwash terraces with the Pinedale glaciation (ca. 14-47 ka). Elsewhere in the northern part of the upper Arkansas Valley, glacial sequences are correlated by mapping outwash terraces near the mouths of major tributaries of the Arkansas River. Near Twin Lakes, indices for soils on low, outer lateral moraines suggest that the older Pinedale glaciers extended beyond the margin of high, younger Pinedale lateral moraines with hummocky topography. A few subdued moraines near Twin Lakes and Leadville probably record one or more glaciations significantly older than the Bull Lake. The downvalley extent of Pinedale glaciers in the Mosquito Range on the east side of the Arkansas Valley is uncertain: most likely, Pinedale glaciers were almost as extensive as Bull Lake glaciers but built no prominent terminal moraines at their maximum positions.

Unusual Amino Acid Determinants of Host Range in the Mtx2 Family of Mosquitocidal Toxins

Five different mosquitocidal toxin (mtx2) gene homologs have been cloned from eight Bacillus sphaericus strains. Pairwise comparisons of the predicted amino acid sequences show between four and eight substitutions compared with the prototype Mtx2 from B. sphaericus strain SSII-1. Mtx2 from strain SSII-1 was approximately 7-fold more toxic to Culex mosquito larvae than the Mtx2 homolog from B. sphaericus strain 31-2. Conversely, Mtx2 from strain 31-2 was approximately 100-fold more toxic to Aedes mosquito larvae than Mtx2 from strain SSII-1. Lys224 in Mtx2 was found to be the most important amino acid for toxicity to Culex larvae, and substitution of Lys224 with threonine abolished the toxicity of Mtx2 from strain SSII-1 to these larvae. In complete contrast, Thr224 was found to be crucial for the toxicity of Mtx2 from strain 31-2 to Aedes larvae, and substitution of Thr224 with lysine caused a approximately 100-fold drop in toxicity to these larvae. Thus, amino acid 224 in the Mtx2 family of mosquitocidal toxins is an unusual and important determinant of mosquito larvicidal activity and host range.

Changes in Vegetation and Soil Fertility along a Predictable Snowmelt Gradient in the Mosquito Range, Colorado, U. S. A.

Changes in edaphic conditions and vegetation along snowmelt gradients are well known in many alpine areas, but very few studies have used multivariate techniques to document these changes at a microgeographic scale and to measure predictability of snowmelt patterns. This paper describes concordant changes in microenvironmental factors and plant species abundances among >200 evenly spaced microsites in a large alpine snowbed in the Mosquito Range, Colorado. The snowmelt gradient was highly consistent: averaged over all microsites, the mean date of snowmelt varied by only 1 wk from 1989 to 1992, and relative date of snowmelt among microsites was highly predictable (R2 > 90% among years). Soil in later melting microsites had reduced organic content, water content, nitrogen, phosphorous, and acidity. Total soil nitrogen and water content decreased through the growing season, while pH increased significantly. Species richness and total vegetation cover were significantly greater in early melting microsites, and soil disturbance by pocket gophers and erosion peaked in moderately latemelting areas. Canonical correspondence analysis (CCA) showed that microgeographic changes in the plant community were associated with four environmental factors: snowmelt date, rock cover, soil disturbance, and soil organic content. Plant species that are common in the vegetation surrounding the snowbed tended to decrease in abundance in later melting snowbed sites. Other species attained peak abundance in the less productive late melting sites, and a few appeared to be associated with soil disturbance. Plant community differences between paired sampling units (quadrats) were determined more by differences in their snowmelt date than by their spatial separation, suggesting that plant species distributions along this alpine gradient are determined principally by ecological interactions and physiological tolerances, rather than by historical accident and limited dispersal.

The Climax-Alma granite batholith of oligocene age and the prophyry molybdenum deposits of Climax, Colorado, U.S.A.

The porphyry molybdenum deposits of Climax, Colorado, are stockworks of quartz-molybdenite veinlets. They are apical to intrusive cupolas of leucocratic rhyolite-granite porphyry of Oligocene age (33 to 24 Ma). The upper parts of the orebodies are overprinted by overlying zones of phyllically altered rocks, and by stockworks of greisen-like veinlets, containing quartz, pyrite, topaz and huebnerite. The phyllic and/or greisen-like zones are surrounded by a propylitic zone, characterized by quartz-chlorite-hematite veinlets and chlorite after biotite. Late veins, radial and peripheral to the intrusive center, are common but widely scattered and discontinuous. Such veins typically contain quartz, fluorite, rhodochrosite, pyrite, dark sphalerite, galena, tetrahedrite, and traces of huebnerite, molybdenite, argentite, native gold and/or electrum. The Alma district, 4 to 10 km southeast of Climax, contains widely scattered clusters of veins and replacement deposits. The veins cut chloritized to sericitized silicate host rocks, and the replacement deposits are in carbonate host rocks. The ore- and gangue-mineral assemblages of the veins of the Alma district resemble those of veins peripheral to the Climax molybdenum deposits. Veins of the Alma district cut dikes of Late white rhyolite (35 Ma), which resemble the rhyolite porphyries of Climax. A swarm of such dikes is parallel to the long axis of an elliptical drainage pattern, which bounds a structural dome, here called the outer Alma dome. The outer Alma dome (8 × 12 km) surrounds an inner Alma dome (6 × 8 km). Veins of the Alma district generally are axial and/or marginal to the outer Alma dome, and/or radial to the inner Alma dome. Veins and alteration minerals associated with the outer Alma dome formed between 35 and 27 Ma ago. Those associated with the inner Alma dome formed about 27 Ma ago, as indicated by fission-track age determinations on thermally annealed zircon grains from hydrothermally altered rocks, within and around the inner Alma dome. Negative Bouguer gravity anomaly patterns indicate: (1) a regional, northeast-trending gravity low, associated with the composite monzonite-granodiorite-granite B batholith of the Colorado mineral belt (average density about 2.62 g/cm 3); (2) a semi-regional gravity trough, within the gravity low of the Colorado mineral belt, extending northeastward across the Mosquito Range; (3) an oval pattern of gravity lows, coincident with the Alma domes; and (4) a closed gravity low associated with the Climax stock (density about 2.56 g/cm 3) (Tweto and Case, 1972; Behrent and Bajwa, 1974; Corry, 1981). The semi-regional gravity trough is interpreted as the gravimetric expression of a granite batholith, here called the Climax-Alma batholith. The gravity lows of the Climax and Alma districts are interpreted as expressions of cupolas on this granite batholith. The highly differentiated rhyolite-granite intrusions of Climax plunge toward the Alma domes. The Climax intrusions are interpreted as products of apical differentiation of the inferred Climax-Alma granite batholith. Magmatic-hydrothermal fluids, associated with highly differentiated apical magmas, produced the Climax molybdenum orebodies. Most of the veins and replacement deposits of the Alma district are associated with lower, broader cupolas of the inferred granite batholith. The shape of the composite Climax-Alma magmatic-hydrothermal system resembles that of a teapot, with Climax above the spout and the Alma district above the lower, broadly domed lid.

Studies on the culicine mosquito host range of Bacillus sphaericus and Bacillus thuringiensis var israelensis with notes on the effects of temperature and instar on bacterial efficacy

Toxicity tests of three strains of Bacillus sphaericus against late instars of 12 culicine mosquito species indicated a wide range of susceptibility. Culex pipiens and C. salinarius were highly susceptible (LC 50 s < 10 4 spores/ml) to strain 1593, and C. pipiens and C. restuans were highly susceptible to strain 2013-4. The potency of strain SSII-1 was approximately one-tenth that of strains 1593 and 2013-4 against C. pipiens. Susceptibility of Aedes species to strain 1593 was highly variable. At temperatures ≥ 20°C, A. fitchii, A. intrudens, A. stimulans, and A. vexans were moderately to highly susceptible (LC 50 s 6 × 10 3−4 × 10 4 spores/ml), A. triseriatus was only slightly susceptible (LC 50 > 10 6 spores/ml), and A. aegypti was refractory. Susceptibility of Aedes mosquitoes to strain SSII-1 was less variable, with LC 50 s against A. aegypti, A. canadensis, A. stimulans, and A. triseriatus all being between 10 4 and 10 6 vegetative cells + spores/ml. All species of mosquitoes tested were, in general, highly susceptible to B. thuringiensis var. israelensis (LC 50 s 2.3 × 10 3−2.5 × 10 4 spores/ml). In B. sphaericus toxicity tests, decreased temperatures resulted in up to a 16-fold increase in LC 50 and a substantial reduction in probit line slope. First-instar A. aegypti larvae were more susceptible to B. sphaericus strain SSII-1 than the three later instars, which were approximately equally susceptible; however, no significant difference was observed in the susceptibility of the four instars of A. triseriatus.

Morphology and the role of landsliding in formation of some rock glaciers in the mosquito range, Colorado : Vick, S G Geol Soc Am Bull, Part 1, V92, N2, Feb 1981, P75–84

Morphology and the role of landsliding in formation of some rock glaciers in the mosquito range, Colorado : Vick, S G Geol Soc Am Bull, Part 1, V92, N2, Feb 1981, P75–84

Morphology and the role of landsliding in formation of some rock glaciers in the Mosquito Range, Colorado

Research Article| February 01, 1981 Morphology and the role of landsliding in formation of some rock glaciers in the Mosquito Range, Colorado STEVEN G. VICK STEVEN G. VICK 1Dames & Moore, Salt Lake City, Utah 84111 Search for other works by this author on: GSW Google Scholar GSA Bulletin (1981) 92 (2): 75–84. https://doi.org/10.1130/0016-7606(1981)92<75:MATROL>2.0.CO;2 Article history first online: 01 Jun 2017 Cite View This Citation Add to Citation Manager Share Icon Share Facebook Twitter LinkedIn MailTo Tools Icon Tools Get Permissions Search Site Citation STEVEN G. VICK; Morphology and the role of landsliding in formation of some rock glaciers in the Mosquito Range, Colorado. GSA Bulletin 1981;; 92 (2): 75–84. doi: https://doi.org/10.1130/0016-7606(1981)92<75:MATROL>2.0.CO;2 Download citation file: Ris (Zotero) Refmanager EasyBib Bookends Mendeley Papers EndNote RefWorks BibTex toolbar search Search Dropdown Menu toolbar search search input Search input auto suggest filter your search All ContentBy SocietyGSA Bulletin Search Advanced Search Abstract Some 23 rock glaciers have been identified in the central portion of the Mosquito Range. Surface features and characteristic forms correlate well with those reported for rock glaciers in Alaska and elsewhere in Colorado, New Mexico, and Utah. On the basis of air-photo interpretation, about two-thirds of the rock glaciers are lobate in form, and one-third are tongue-shaped. Only 5 of the 23 rock glaciers are believed to be active.A detailed stability analysis of two rock glaciers in Iowa Gulch indicates that landsliding of unstable morainal deposits played a major role in their formation. Landslide debris provided loading necessary to initiate ice creep in frozen till on the lower valley slopes. Ice creep continued, eventually bringing the rock glaciers to their present form. With the supply of landslide debris exhausted and with insufficient ice wedging and rock exposure to generate large talus cones, stresses generated by the superincumbent load were reduced by creep-induced spreading, and motion ceased. Internal ice, in the form of both interstitial ice and ice layers, still remains.Techniques developed to evaluate activity of rock glaciers in Alaska have been applied to the two rock glaciers in Iowa Gulch. These techniques, based principally on steepness and form of the rock glacier front as well as on calculated values of basal shear stress, indicate both rock glaciers to be inactive. Re-survey of a mining claim corner and inspection of a shaft show that no movement has occurred over the period of record and that the rock glaciers are indeed inactive, substantiating the usefulness and validity of the above-described techniques for assessment of rock glacier activity elsewhere. This content is PDF only. Please click on the PDF icon to access. First Page Preview Close Modal You do not have access to this content, please speak to your institutional administrator if you feel you should have access.

Structure, petrology, and petrogenesis of the Treasurevault stock, Mosquito Range, Colorado

The Treasurevault stock intrudes high-grade metamorphic rocks approximately 10 km east of Leadville, Colorado, in the northern Mosquito Range. The stock is roughly circular in exposed plan and about 3 km in diameter. It consists of quartz monzonite that is remarkably uniform in mineralogical and chemical composition. Three textural facies occur in roughly concentric zones: medium-grained rocks occur between fine-grained rocks at the contacts and coarse-grained rocks near the center of the stock. Primary flow structure near the contact suggests that the upper part of the stock is hemispherical. Primary radial and diagonal joints are well developed near the contact. Both flow structures and joints probably formed just before and after consolidation as a result of compression perpendicular to contacts. The K-Ar age of the stock is 1,430 ± 45 m.y. (Precambrian Y), indicating emplacement during the Silver Plume magmatic event. A model for the petrogenesis of the Treasurevault stock includes derivation of the parent magma by partial melting of lower crustal rocks at a depth of ∼40 km, emplacement of the magma due to gravitational instability to a depth of ∼10 km, and crystallization of most of the magma under conditions of water undersaturation. A water-saturated pegmatite magma developed after more than 97 percent of the stock had crystallized.

Paleozoic Stratigraphy of the Franklin Mountains of West Texas: ABSTRACT

The Franklin Mountains are located within a region that is bounded on the east by longitude 104°30^prime W., on the west by longitude 109° W., on the south approximately by latitude 31° N., on the north approximately by latitude 34° N. From just north of El Paso the Franklin Range trends almost parallel with the 106°30^prime meridian to a point about 4 miles north of the Texas-New Mexico boundary line. The Franklin Mountains are eroded block mountains typical of the basin-and-range structure of the southwestern United States. The west side is a steep dip slope developed principally on beds of limestone. The east side is a fault scarp. The Paleozoic stratigraphic section, which aggregates 5,600-7,000 feet in thickness, is as follows: Permian, Wolfcamp formation; Pennsylvanian, Magdalena formation; Mississippian, Helms formation; Devonian, Canutillo formation; Silurian, Fusselman limestone; Ordovician, Montoya and El Paso limestones; Cambrian, Bliss sandstone. The section is overlain by the Comanche and rests, in places, on pre-Cambrian granite and at other places on the Llanoria quartzite. End_Page 1704------------------------------ The exposed portion of the Magdalena formation consists primarily of thin-bedded, light gray to black limestone, and for convenience it is divided into the following three units: the La Tuna at the base, the Berino, and the Bishop's Cap at the top. Comparatively few fossils have been reported from the near-by localities; hence it is difficult to use them to correlate the Magdalena of the Franklin Mountains with formations in these areas. A few closely allied genera and species of gastropods and brachiopods are reported from the Taos region of northern New Mexico and from the McCoy region and the Mosquito Range of Colorado. However, the most striking similarity is to a gastropod fauna described from the St. Louis outlier of Missouri and the equivalent St. David's limestone of Illinois. The Permian is represented by about 650 feet of exposed sediments known as the Wolfcamp. These sediments occur as outliers some distance west of the Franklin Range and are separated from the exposed Magdalena sediments by alluvial deposits; hence the contact between the Magdalena and the Wolfcamp has not been seen. End_of_Article - Last_Page 1705------------

Stratigraphy and Structure of Pennsylvanian and Permian Rocks in Salt Creek Area, Mosquito Range, Colorado

The Pennsylvanian and Permian sediments of a region in central Colorado are described in regard to their areal extent, lithologic characteristics, stratigraphic relations, and geologic age. Several stratigraphic units are mapped. Three of these are established as new members of the Maroon formation, namely, the Coffman conglomerate member of Pennsylvanian (?) age, and the Chubb siltstone and Pony Spring siltstone members of Permian age. The structure of the rocks in this area is discussed, a major contribution being the extension of the Trout Creek fault approximately 8 miles along its trace beyond its previously known location. An interpretation of the geologic history of the area is given, as determined from petrographic and stratigraphic evidence. It is concluded that he Weber (?) formation (Pennsylvanian), composed chiefly of shale, was deposited in a dominantly neritic, but at places littoral, environment; that the Coffman, consisting of arkosic conglomerate, sandstone, and shale, was formed in a delta and flood-plain environment; that the Chubb, composed of siltstone with arkosic sandstone in the upper part, originated under fluviatile conditions on coalescing flood-plains; and that the Pony Spring, consisting of siltstone with interstratified sandstone and shale, was also formed in a flood-plain environment.

Insoluble Residues from Paleozoic Limestones of the Mosquito Range, Colorado

ABSTRACT The general characteristics of insoluble residues from five dolomitic limestone units, in the Paleozoic formations of the Mosquito Range, are described. In general, isolated residues from these formations have little diagnostic value, but groups of residues from several beds within a narrow stratigraphic range have distinctive features that furnish a valuable and readily utilized aid in correlation.