Recurrent Movement Research Articles

Tectonic Influence on Sedimentation of Lower Cretaceous Strata, East-Central Powder River Basin, Wyoming: ABSTRACT

Recurrent movement of basement fault blocks in the east-central Powder River basin has controlled the distribution of porous and permeable reservoir facies within Lower Cretaceous strata. Subsurface isopach data for Lower Cretaceous time-stratigraphic intervals show repetitive thickness variations for both marine (Skull Creek and Mowry shales) and nonmarine (Inyan Kara and Newcastle/Muddy sandstones) units. Thickness patterns seem to be controlled by recurrent Early Cretaceous structural movement. Paleostructures ranging in width from 2 to 10 mi (3.3 to 16.6 km) and in length from 10 to 30 mi (16.6 to 50 km) trend northeast, northwest and north, and include segments of the Black Hills and Fanny Peak monoclines, which bound the west flank of the Black Hills uplift. Early Cretaceous paleostructures seem to control the distribution of Newcastle valleys which are incised into the underlying Skull Creek Shale and drain southwest and northwest (corresponding to the Clareton, Hilight, Osage, Fiddler Creek, and Rozet fields). Alluvial plain valley-fill deposits in Newcastle Formation outcrop show abrupt facies and thickness changes which coincide with evidence of structural control (e.g., drape folds, faults, sandstone dikes, geomorphic lineaments, and increased igneous activity). A depositional model, incorporating tectonic and sea-level adjustments, illustrates that Newcastle channel incisement and valley fill are generally restricted to topographic and structural low (graben) areas. This model has been confirmed by detailed analysis of seismic data. /P> A model for tectonic influence on sedimentation aids in petroleum exploration by helping to predict facies distribution and fluid flow. End_of_Article - Last_Page 567------------

Estimates of vertical crystal strain rates along the western margins of the Colorado Plateau

Dating of basalts of late Cenozoic age that have been displaced by recurrent movement along fault systems of the western Colorado Plateau indicates that perennial streams downcut quickly after uplifts. The rate of downcutting of the offset basalts upstream from a fault is largely a function of the amount of uplift. Minimum uplift rates can be estimated by comparing present stream profiles to the profiles that existed before extrusion of the lava flows. A preliminary study of the valleys of the Virgin River and adjacent drainage systems indicates that the eastern margin of the Basin and Range province has been rising in relative altitude at roughly 25 m/m.y. in the Grand Wash area, at least 90 m/m.y. in the block between the Grand Wash and Hurricane faults, and 390 m/m.y. in the block east of the Hurricane fault.

Upper Cretaceous Stratigraphy and Tectonic History of Ridgway Area, Northern San Juan Mountains, Colorado: ABSTRACT

Detailed mapping and stratigraphic studies in the Ridgway area, along the northern flank of the San Juan Mountains in Colorado, indicate that the lower Mancos Group (Upper Cretaceous) can be subdivided into four formations. From oldest to youngest, they are the Benton Formation, Juana Lopez, Sage Breaks Shale, and Niobrara Formation. These formations have lithologic and paleontologic content similar to their equivalents in the Denver and San Juan basins and Black Hills. The underlying Benton Formation consists of 470 ft (143 m) of black shale that includes the Greenhorn Limestone Member (12 ft or 3.5 m thick) lying 300 ft (91 m) above the base. The overlying Juana Lopez is 40 ft (12 m) thick and consists of alternating layers of calcareous siltstone and black shale. The succeeding Sage Breaks is a 155-ft (47 m) calcareous shale unit. The overlying Niobrara Formation is an 85-ft (26 m) resistant, cliff-forming, calcareous shale. Subsurface and outcrop data in the south indicate that the study area straddles the margin of the Pennsylvanian Uncompahgre uplift. Structural evolution has been controlled largely by three east-west trending Precambrian fault blocks--the Ouray graben, the Orvis block, and the Uncompahgre block. Recurrent movement of these fault blocks from the Paleozoic through the Cenozoic affected both sediment thickness and facies distribution. A cross section restored to the base of the Dolores Formation (Upper Triassic) indicates that the Permian End_Page 572------------------------------ Cutler Formation increases 1,050 ft (320 m) in thickness across the Orvis fault, which had down-to-the-south movement. During the Laramide orogeny, a significant reversal in movement occurred along the fault to cause the north-dipping monocline now present at the surface. End_of_Article - Last_Page 573------------

Relation of Unconformities, Tectonics, and Sea Level Changes, Cretaceous of Western Interior, United States and Canada: ABSTRACT

Intrabasin tectonics have influenced patterns of deposition and geographic distribution of major unconformities within the Cretaceous of the Western Interior. Eight major regional to subregional unconformities have been identified. Five of these have been related by previous workers to sea level changes and to well-documented regressive-transgressive cycles. New studies of recurrent movement on basement-controlled fault blocks suggest a synchronous relation among fault block movement, sea level changes, and unconformities. Which fault blocks moved on the basin floor, and when, can be explained by stress fields generated by direction and rates of plate motion. Unconformities associated with north-northwest fault trends are caused by more westerly movement, and those associated with east-northeast trends by more northerly plate motion. Expansion of the Gulf of Mexico, the Atlantic Ocean, or the Arctic Ocean during these plate motions may account for associated sea level changes. The 81 to 82 m.y. unconformity and shoreline regression in the Western Interior and synchronous volcanic events on the northern margin of the Gulf of Mexico illustr te the relations. Uncertainty exists in dating many of the unconformities. However, by use of the time scale of Obradovich and Cobban, the approximate dates for unconformities are estimated as follows: (1) late Neocomian to early Aptain, >100 m.y.; (2) late Aptian-early Albian, 100 m.y. ±; (3) Albian, 96 to 97 m.y.; (4) early Cenomanian, 93 m.y. ±; (5) Turonian to early Coniacian, 87 to 88 m.y.; (6) late Coniacian-early Santonian, 81 to 82 m.y.; (7) late Campanian 71 to 74 m.y.; and (8) late Maestrichtian, 64 to 69 m.y. Several billion barrels of oil have been found in sandstones associated with unconformities in the Cretaceous. Future stratigraphic trap exploration will be guided by a knowledge of tectonic influence on sedimentation during sea level changes and how these factors controlled distribution of source rock, migration patterns, reservoir rock, and seal. End_of_Article - Last_Page 1006------------

Wattenberg and Spindle Fields--Paleostructural and Stratigraphic Traps, Denver Basin, Colorado: ABSTRACT

The most important mineral resource activity in Colorado during the past decade has been the discovery and development of the Wattenberg gas field and the shallow overlying Spindle oil and gas field. Located north of Denver near the axis of the Denver basin, Wattenberg is estimated to have reserves of 1.3 Tcf of gas in the tight J sandstone (delta front) reservoir over an area of 600,000 acres (240,000 ha.), at depths of 7,600 to 8,400 ft (2,316 to 2,560 m). Spindle field, in the south-west part of the Wattenberg field, produces from two marine sandstone bar complexes (Terry and Hygiene Sandstones) in the middle part of the Pierre Shale. From an area of 30,000 acres (12,000 ha.), total production is in excess of 28,000,000 bbls of oil and 100 Bcf of gas at depths of 4,0 0 to 5,000 ft (1,219 to 1,524 m). Although both fields are regarded as stratigraphic traps, paleostructural analysis of the area clearly shows that during middle Cretaceous the fields were located on an ancient structural high that was subsequently downwarped into the present low structural setting. Evidence for recurrent movement on the paleohigh are unconformities at the top of the J sandstone and at the base and top of the Niobrara Formation, and also thinning of shale intervals and localization of marine sand bars within the Pierre Shale. The outline of the Wattenberg paleostructure is best shown by the area of truncation by erosion of the upper chalk of the Niobrara Formation over an area 10 mi wide × 50 mi long (16.1 km × 80.5 km). The east-west trend of the paleostructure changes to northeast and extends for more than 100 mi (16.1 km) into western Nebraska. Three other similar paleostructural trends can be mapped in the northern Denver basin. Knowledge of paleostructural control on reservoir facies and petroleum migration provides new ideas for petroleum exploration in Cretaceous rocks and in the deeper Paleozoic section of the Denver basin. End_of_Article - Last_Page 801------------

Influence of Basement Tectonics on Depositional Systems and Seismic Stratigraphy: ABSTRACT

The new field of seismic stratigraphy has focused attention on the reconstruction of depositional models in which seismic responses can be evaluated and interpreted. In many exploration programs, geologists and geophysicists limit their work to processing data from relatively thin petroleum-productive sequences. Amplitude and other seismic anomalies and porosity variations are studied in search for the elusive stratigraphic trap without concern for what geologic conditions are present at the deeper basement level. Current research in oil-productive basins indicates that recurrent movement on basement fault systems during deposition may have had an important influence on the distribution of reservoir rock, on early fracture systems controlling petroleum migration, and on other subtle trapping mechanisms. The concept of drape folding over basement faulting can be related to the concept of fault control of facies changes. Therefore, establishment of fault trends in the basement may aid in predicting stratigraphic traps. Using this approach, success in exploration may be improved by developing exploration models which incorporate basement level tectonics with stratigraphic and seismic anomalies occurring at shallower depths. End_of_Article - Last_Page 550------------

Stafford fault system: Structures documenting Cretaceous and Tertiary deformation along the Fall Line in northeastern Virginia

Four en echelon northeast-trending structures, including southeast-dipping monoclines and northwest-dipping, high-angle reverse faults, have been mapped along the inner edge of the Coastal Plain in northeastern Virginia–an area generally considered to be undeformed. Although displacements are small (15 to 60 m), the structures markedly affect the present distribution and thickness of Coastal Plain sediments. Structure-contour maps on Cretaceous and Paleocene lithostratigraphic units show that the amount of displacement on the structures increases downward, indicating recurrent movement. The major deformation took place in the Cretaceous and the middle(?) Tertiary, but some latest Tertiary or Quaternary movement is possible. The structures, herein named the Stafford fault system, extend for at least 56 km parallel to the Fall Line and the northeast-trending reach of the Potomac estuary. This relationship supports the hypothesis that the Fall Line and major river deflections along it have been tectonically influenced.

Holocene faulting in the western Grand Canyon, Arizona

The Toroweap and Hurricane faults and a subsidiary fault in the western Grand Canyon exhibit evidence of Holocene movement. This evidence includes scarps in alluvium and sediments ponded against a fault on the downthrown block. These displacements are the latest in a well-exposed record of recurrent movements along the major faults in the region.

Patterns of displacement along the Wasatch fault

Patterns of recurrent movement along the Wasatch fault are indicated by the size and spacing of pediment remnants preserved at the apices of successive generations of faceted spurs. A preliminary study suggests that movement occurred along the fault until 200 to 300 m of vertical displacement were produced; this movement was followed by a period of quiescence. For the southern part of the fault, eight periods of nearly continuous movement were apparently separated by relatively short periods of stability. Northward, the pattern changes to one with fewer periods of active displacement separated by longer periods of quiescence during which little or no displacement occurred. The results suggest that during late Cenozoic time the Wasatch fault has experienced a history of recurrent displacement.

Geologic Structures in Northern California as Detected from ERTS-1 Satellite Imagery

Repetitive multispectral ERTS-l (Earth Resources Technical Satellite-1) imagery of northern California has disclosed several systems of linear features that may be important for the interpretation of the structural history of California. Four linear systems coexist within the northern Coast Ranges. They are separated from an orthogonal system of linear features in the Klamath Mountains by a set of discontinuous east-southeast–trending linear features (the Mendocino system) which are traceable from the Pacific Coast at Cape Mendocino into the eastern foothills of the Sierra Nevada. Within the Sierra Nevada, the Mendocino system separates the north-trending Sierran system from a set characteristic of the Modoc Plateau. With minor exception, little overlap exists among the systems, which suggests a decipherable chronology and evolutionary history for the region. The San Andreas system of linear features appears to truncate or coexist with most other systems in the northern Coast Ranges. The Mendocino system truncates the Klamath, Sierran, and Modoc systems. The Sierran system may represent fundamental and long-persisting early to mid-Mesozoic zones of crustal weakness which may have been reactivated during late Mesozoic time. The Mendocino system was possibly developed during mid- to late Mesozoic time, and recurrent movement has persisted into the Holocene Epoch. The Mendocino system is thus an important element in the structural framework of northern California.

Chorea associated with systemic lupus erythematosus. Treatment with haloperidol.

Chorea is a rare manifestation of systemic lupus erythematosus. Treatment with haloperidol of such a condition in an 18-year-old woman resulted in a prompt and complete subsidence of symptoms in contrast to previous episodes without haloperidol lasting as long as three months. Recurrent choreiform movements nine months later responded similarly.

Deltaic Sedimentation and Growth Faulting, Upper Cretaceous, Colorado: ABSTRACT

The upper Pierre, Fox Hills, Laramie, and Arapahoe Formations in the western Denver basin record deltaic sedimentation during the final regression of the Cretaceous sea from eastern Colorado. Prodelta shales and siltstones (Pierre Formation) are overlain by delta-front sandstones (Fox Hills), and delta-plain sandstones, claystones and coals (Laramie Formation). The younger conglomerates of the Arapahoe Formation are braided channel deposits of the fluvial system. Two types of penecontemporaneous (growth) faulting are recognized in 5 mi of outcrop from Golden south to Interstate 70. One type of faulting cuts delta-plain sediments, resulting in a thickness increase of the Laramie Formation from 330 to 530 ft in a horizontal distance of 800 ft. By normal fault movement at the time of sedimentation, an extra 200 ft of lower Laramie sandstone, with minor claystone and thin coal, was deposited on the downthrown side of the fault. The northwest-trending fault plane curved downward toward the south from a dip of about 60° to a low-angle bedding plane fault. A second type of faulting records slumpage on oversteepened prodelta slopes created by seaward progradation of the shoreline. One slide block of shallow-water distributary-mouth sandstone (Fox Hills) about 100 ft thick moved southward down the prodelta slope into water depths estimated to be from 100 to 175 ft and was subsequently buried by prodelta clays (Pierre). The geographic position of these growth faults in the delta sequence appears to have been controlled by recurrent movement of deep-seated faults in the Precambrian basement which at the time of Laramie deposition was at depths in excess of 10,000 ft. Growth faulting heretofore unrecognized in the Cretaceous of the Rocky Mountain area, may be a common occurrence in the areas of deltaic sedimentation. Some abrupt thickness changes may be explained more readily by this process than by the commonly invoked theories of facies change or unconformities. End_of_Article - Last_Page 661------------

Ground-Water Quality and Structural Control in Southeastern Virginia

Investigations into the stratigraphy, structure, piezometric surfaces, and ground-water chloride concentrations of the York-James peninsula and adjacent Coastal Plain areas to the south indicate that these geologic factors display a mutual dependence. North-south e-log correlations across the area support existence of the proposed Hampton Roads fault in the vicinity of the James River. Isochlor contours trend subparallel to the James River in the York-James peninsula, and piezometric surfaces show a marked dissimilarity on either side of this river boundary. The high chloride concentrations in this area, plus the disruption of the ground-water system, imply fault control and incursions of saline waters along the Hampton Roads fault zone during times of recurrent movement. A similar situation exists near the confluence of the James River with the Chesapeake Bay, where a disrupted piezometric surface and a high chloride zone are found in conjunction with a proposed north to north-westerly trending fault zone, the Norfolk Hinge. Highest chloride concentrations, greatest disruption of the piezometric surface, and greatest stratigraphic displacement occur near the intersection of these two faults.

Pre-Pennsylvanian Paleotectonic Framework of Ancestral Rockies of Colorado: ABSTRACT

The tectonic framework that controlled the locations of the late Paleozoic Ancestral Rockies was well established in pre-Pennsylvanian time. The Uncompahgre uplift in southwestern Colorado arose along tectonic lineaments that originated in the late Precambrian. Recurrent movements along the fault system continued through early and middle Paleozoic time and the resulting submarine topography controlled the sedimentation of reservoir facies in the adjacent Paradox basin. The Front Range and Wet Mountains uplifts of central Colorado were apparently low and inactive prior to Late Devonian time; at least, evidence is lacking that they were source areas during the early Paleozoic. The relation between basement tectonic trends and the location of the Permo-Pennsylvanian uplifts is obscure. The first demonstrable uplift of the Front Range element occurred in Late Devonian time when coarse clastic material was shed into the Parting sea from the west flank of the uplift and a satellite structure in the northern Sawatch Range. Uplift of these source areas recurred in Early Mississippian time and produced limestone conglomerates in the basal Leadville Formation. The Wet Mountains lay dormant until Early Mississippian time, and a broad lowland occupied the general region in the Late Devonian. Local deposits of limestone conglomerates in the Leadville Formation attest to the Early Mississippian time of uplift. Continued detailed petrologic and paleotectonic studies in the 1970s will lead to new petroleum discoveries in the related Paradox and Eagle basins by establishing favorable reservoir facies trends, paleohydrodynamic patterns, and times and paths of petroleum migration. End_of_Article - Last_Page 834------------

Penecontemporaneous Downdip Slump Structures in Middle Ordovician Limestone, Harrisonburg, Virginia: GEOLOGICAL NOTES

A fascinating array of penecontemporaneously formed, downdip slump structures is present in the very fine-grained Middle Ordovician Edinburg Limestone near Harrisonburg, Virginia. Two zones of extremely disharmonic, soft-rock flowage folds, separated by an undisturbed zone, attest to recurrent movement. Four inclusions of limestone as much as several feet in diameter are present stratigraphically lower. The transport of three is indicated by differences between them and the host limestone in both lithology and orientation of the bedding surfaces. The fourth mass appears to be rooted but sharply rotated. Still lower stratigraphically are two zones of cross-bedded limestone whose foreset beds represent the accumulation of carbonate muds on a slope that was growing rapidly n rthwestward, the direction of present tectonic dip. The original dip of the crossbeds of the thicker (15 ft) zone may have been as much as 16° but, as a result of slumping downdip, some of the beds of this very disturbed zone show an 83° downdip angle with the master bedding planes. The features are on the northwest limb of the Linville anticline about halfway between its crest and the trough of the adjacent Broadway syncline. The recurrent slumping indicated by these features is attributed to the development of a slope on the flank of the growing anticline that was great enough to induce flowage and slumping of hydroplastic, precipitated carbonate muds. It is no mere coincidence that the basal Middle Ordovician New Market Limestone is unconformable on the Beekmantown Dolomite on the crest of the Linville anticline, whereas an abnormally thick section of this carbonate precipitate lies conformably on the dolomite in the Harrisonburg syncline, adjacent on the southeast, and an equally thick section overlies the Beekmantown Dolomite in the Broadway syncline, adjace t on the northwest.

Geophysical Study of the Keota Dome—Keokuk and Washington Counties, Iowa

The presence of a Paleozoic high in the vicinity of Keota, Iowa, is indicated on structural maps of the Iowa Geological Survey. Stratigraphic test drilling by Natural Gas Pipeline Company of America defined a “butterfly”-shaped structural dome which covered about 30 sq miles. A small amount of petroleum has been produced from the northeast segment of the dome. Closure on this segment is about 120 ft over a length of 3 miles. A geophysical study reveals ground-magnetic and gravity anomalies having amplitudes of from 200 to 400 gammas and from 2 to 3 mgals, respectively, associated with the dome. Polynomial trend-surface analysis of the geophysical data indicates a near-coincident relationship between the low-order residual anomalies and the closure of Keota dome. Interpretation of these data suggests that the structure may possibly be due to recurrent movement during Paleozoic time along a Precambrian fault which was also the locus of Precambrian intrusive igneous activity. The possibility of draping of sediments over a Precambrian topographic high should not be discounted. On the basis of geophysical data and Stratigraphic considerations, the top of the crystalline complex is estimated to be between 3000 and 3500 ft below the surface. It is concluded that ground-magnetic and gravity surveys can be used to locate similar structures in southeastern Iowa. One such structure might occur in the vicinity of the magnetic high south of the village of Talleyrand.

Structural Development of the Williams Range Thrust, Colorado

An area in southwestern Middle Park, Colorado, has been studied in the field. Mapped principal structural features include the Williams Range thrust and a major normal fault east of the thrust. Direct observation of a cross section of the thrust surface, data on its elevation and its trace, an observation of its dip, and an observation on rotation of strata in the overblock show that the thrust surface is curved, being nearly horizontal in its westernmost exposures with progressively steeper eastward dips to the east. The mapped structural features postdate deposition of the Pierre Formation, and the thrust is known to have experienced recurrent movement. This paper explains the development of the mapped principal structural features in terms of a system of stresses acting on the boundaries of the area. Because east-west cross sections are similar, an explanation is offered for an average cross section of, specifically, height equal to 6500 feet and length equal to 32,500 feet. Analysis is treated as a two-dimensional problem. The system presented consists of a combination of two systems of stresses. One is characterized by a step displacement of the midpoint of the lower boundary, the other by a cosine displacement of the lower boundary. The analysis assumes that stress within the body is describable by methods of theory of elasticity and that faults and stress are related by the Mohr criterion. The analysis also assumes that faulting does not affect the orientation of principal stresses as described at the instant prior to inception of faulting and that it tends to increase the magnitudes of stress near its tip and decrease them where faulting has transpired. The system accounts for the attitude of faulting in the average cross section and predicts fault development where faulting has occurred. The explanation is compatible with lesser structural features of the overblock of the area, including high-angle faulting at the north and synclinal development in the youngest Tertiary rocks between the thrust and major normal fault. The explanation is compatible with the regional structural geology and is geologically practicable.

Origin of “Reverse Drag” on the Downthrown Side of Normal Faults

“Reverse drag,” also called “downbending” or “turnover,” was first recognized by Powell in the Colorado Plateau and subsequently was found to be an important structure associated with “down-to-basin” faulting in the Gulf Coast region. Many conflicting hypotheses have been proposed to explain this structure, most of which are based upon subsurface studies or observations in local areas. Detailed field studies of reverse drag made in the western Colorado Plateau reveal that the flexure extends practically the entire length of most normal faults in the region. It is characterized by a broad, asymmetrical arc on the downthrown block, approximately 1 mile wide, with maximum dips of more than 30 degrees near the fault plane. Normal drag is common adjacent to the fault on both the upthrown and downthrown blocks. Reverse drag has been formed repeatedly during recurrent movement along the Hurricane and Grand Wash faults, clearly indicating that it is genetically related to faulting. The magnitude of the flexure is roughly proportional to displacement, and the trend of the fold closely parallels the trend of the fault. In many places reverse drag passes both vertically and laterally into antithetic faults. Observations in the Grand Canyon reveal that the dip of the faults with which reverse drag is associated decreases with depth. It is concluded that reverse drag results from an alternate response to the same forces that produce antithetic faults and develops because of curvature of the fault plane at depth. Normal movement along a curved fault plane, in effect, tends to pull the blocks apart as well as to displace them vertically. Adjustments to fill the incipient gap by rupture produces antithetic faults, whereas failure by flexing develops reverse drag.

Basement Control in the Structural Evolution of Southern Oklahoma: ABSTRACT

Southern Oklahoma comprises a complex of structural elements that can be related to recurrent movement on a system of basement faults that had its origin at the time of consolidation of the crystalline basement. Repeated trans-current movements, accompanied by uplift of horsts and deep subsidence of adjacent grabens delineated by this major fault system, have exerted a profound control over the stratigraphic and structural evolution of southern Oklahoma. The larger faults, the Meers fault of the Wichita Mountains, the Washita Valley and Sulphur faults of the Arbuckle Mountains, and the Choctaw fault of the Ouachita Mountains dominate the minor faults and delineate the major basement blocks, namely, the 4 Wichita block, the Tishomingo-Belton uplift, and the frontal edge of the Ouachita Mountains and the intervening basins. The interplay of these basement controlled blocks and their adjacent grabens has not only influenced sedimentation by establishing the pattern of basin development but they controlled the magnitude and type of tectonism that has occurred throughout the Paleozoic Era. Transcurrent movement, according to the wrench-fault mechanics of Moody and Hill, on the major faults which border the basement blocks has produced the stress field responsible for the structural complexity produced during the several stages of the orogenic climax in late Paleozoic time. End_of_Article - Last_Page 551------------

The Basic Concept of Professor Hart's Jurisprudence

There are but a few days—of who shall say what importance—between the Julian and Gregorian calendars, considered as schemes for the interpretation of recurrent movements in our solar system. And yet, from the point of view of each, the other seems somewhat out in respect of the characterisation of nearly every year, month, week and individual day. The gap between the legal theories of John Austin and Professor Hart—between their models of the legal universe—is somewhat more than this. Its demonstration provides the foundation for Professor Hart's new book. But there may here be some analogy to what divides the concept of law, as elucidated by Professor Hart in terms of rules, from the concept of law as a system of action constructed by the writer in earlier numbers of this Journal. If Professor Hart now reveals himself as conceptual pragmatist as well as linguistic philosopher the writer's gratitude to Professor Hart in the latter capacity is only tinged with regret that he does not display greater boldness in the former.