USA > Colorado > History of the State of Colorado, Volume II > Part 5
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NORTHERN COLORADO FIELD.
This field, as here defined, is a strip forty miles wide, extending from the Wyoming line southward to Franceville, and having a total area of about 6,800 square miles. It does not include the entire extent of Lar- amie rocks, nor yet more than a portion of the immense tract in North- eastern Colorado represented as coal land on Hayden's economic map. Here we again meet with the necessity of establishing a line between what may reasonably be considered coal land and adjacent areas of barren or utterly worthless measures ; and since the change from one class to the other is not abrupt but gradual, and takes place at inaccessible depths, there is room for considerable difference of opinion as to where this line should be drawn. The limit here suggested, of a line forty miles east of the western outcrop, and having the same general contour, will, it is thought, approximately define the extent of the coal basin in Northern Colorado; for while it is known that workable seams are nowhere exposed along the eastern border of the Laramie, thin beds
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HISTORY OF COLORADO.
which may eventually be worked for local consumption, are exposed at both the northern and southern extremities of the field at a distance of about forty miles from the western margin.
All of the accessible outcrop north of Boulder is but slightly inclined, as also most of that in the vicinity of Erie, Louisville, and Lang- ford. In the neighborhood of Franceville and Colorado Springs the inclination is from 7° to 10° with a tendency to flatten out away from the great fold of the Front Range. The remainder of the outcrop, or that lying contiguous to the mountains, is upturned from 40° to 80°.
In what may be termed the Franceville district, the workable coal ranges from six to ten feet in thickness. Along the highly inclined out- crop, and in the Boulder County districts the aggregate thickness is greater ; but in the more northern part of the field the beds thin out, being only three to four feet thick at Plattville and Eaton.
All the coal from the Northern Colorado field is intermediate in char- acter between lignite and cherry-coal, in composition approaching the former ; in structure and appearance, the latter. The principal ob- jection that can be urged against it is its capacity for absorbing moisture, which varies from twelve per cent. in that from the Boulder County dis- tricts, to over twenty per cent. in the more inferior qualities from other districts. Such hygroscopic coals invariably disintegrate on exposure for a short time to the atmosphere, for which reason they are poorly adapted for either storage or exportation. At the same time they find a ready sale in the nearest markets on account of their cheapness.
The amount of available coal which this field may contain, is not easy to estimate. Notwithstanding the thinning out of the beds in the northern half, their accessibility, even in places far to the east of the out- crop, coupled with the requirements of the treeless region in which some areas are situated, may eventually render profitable the working of quite thin seams. What the limit will prove to be can hardly be conjectured, and for the present must be taken at the thickness that can be mined under existing conditions.
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HISTORY OF COLORADO.
The districts lying in Boulder County contain a number of small tracts, of slightly inclined measures, separated from one another by faults or abrupt flexures, whose origin is to be referred to the dynamic movement accompanying the final elevation of the Front Range, and a certain amount of eruptive activity indicated by the Valmont dyke. This part of the measures affords the best quality of coal in the Northern Colorado field; hence, notwithstanding the disturbance to which much of the ground has been subjected, it will no doubt be thoroughly exhausted before abandonment.
The upturned measures probably contain the greatest aggregate thickness of coal so far as one can judge from the limited amount of exploration, yet for several reasons they can hardly be considered economically accessible below a depth of half a mile. The extreme southern part of the field possesses on the whole the most merit, except in the quality of the product. The coal is of fair workable thickness, while the slight inclination of the beds renders it possible to mine it eco- nomically for several miles back of the marginal outcrop. There is also a noticeable absence of abrupt folds, faults, and displacements, such as are common in the Boulder County districts, and which are a serious obstacle to extended continuous operations.
While the Northern Colorado field contains a vast quantity of available coal, and has the advantage over all our fields of nearness to markets, the inferiority of the product places it below both the Grand River and Raton fields in importance to the State,-a fact which will become more and more evident as the country develops.
NORTH PARK FIELD.
This field, like the Yampa field, has been but little explored, and up to the present time no systematic work on the seams has been attempted. The measures extend from the northeastern border of the North Park basin,-where there are exposures of coal between the Canadian and Michigan Rivers,-as far south as Grand River in Middle Park, where very thin streaks of coal are met with around Hot Sulphur Springs.
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HISTORY OF COLORADO.
The measures of economic value are, however, restricted to the North Park basin and the region on the head of Muddy Creek around Mount Wheatly. The most accessible part of the field, and that which contains by far the greatest aggregate thickness of coal, is the northern extremity. Between the Canadian and Michigan the measures are brought to the surface by an anticlinal flexure, from the apex of which they dip in opposite directions about 15°. To the northeast of this flexure there is a synclinal depression, about three miles broad, termin- ating in the marginal outcrop, where the beds again come to the surface. For a distance of about twelve miles along this outcrop seams of lignite- coal are exposed naturally or by excavations. There are apparently three workable beds in this part of the field,-the Red Hill seam, from twenty-one to thirty-two feet thick, the Coal Hill seam, fifteen feet thick, and the Walden seam, four to five feet thick ; all of which are remark- ably free from shale and other impurities.
The composition of North Park coal is decidedly lignitic, the moist- ure retained ranging from twelve per cent. to eighteen per cent., in which respect it corresponds to the coals of the Northern Colorado field, although when first extracted it is black and lustrous like ordinary soft coal, hence the term, "lignite-coal" to distinguish it from true lignite, which is not known in Colorado. The estimate of available coal in this. field, given beyond, is not based on a thorough exploration of it : conse- quently, the figures are merely suggested as probably within reasonable limits.
OTHER DISTRICTS.
The areas of coal land remaining to be noted embrace those isolated districts which cannot be included in any of the great fields; at the same time they are severally too limited in extent to be treated as so many independent fields. These are the South Park, Canon City, and Tongue Mesa, districts. They are estimated to contain collectively fifty square miles of available measures.
The South Park district includes the mines which, for a number of years, have been systematically worked near Como. The principal seam
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HISTORY OF COLORADO.
is from five to six feet thick, and produces a strongly coking-coal of fair quality; probably the best mined in Northeastern Colorado. The measures have been considerably disturbed in the vicinity of the mines, but the district may develop better ground when its capabilities shall have been further investigated.
The Canon City district is the best known of the three, having for years produced a very superior variety of domestic fuel, which finds a ready sale in the market, and has served to establish the importance of the vast reserves of this kind of coal so abundant in the measures of Western Colorado, and in the northern part of the Raton field. Most of the Canon City coal is taken from a seam about five feet thick, having usually a varying thickness of shale toward the center, and is mined from a number of openings on Coal Creek and Oak Creek, about four miles southward from Florence. Along the western border of the district the beds are upturned at a high angle, but flatten rapidly toward the eastward, and over the greater part of the area the measures are but slightly inclined, so that nearly the whole will in time be made available.
Tongue Mesa district includes a long, narrow strip of land, elevated and capped with lava, lying between the Cimarron and Uncompahgre Rivers. There are four workable seams ranging from five to twenty feet in thickness, reported as outcropping on the south side of the Mesa. A small amount of coal has been mined for local consumption ; but the location is too remote, and the quality of the product, so far as known, too inferior to make it desirable as an export fuel. Like the bulk of Western Colorado coal, it is semi-coking, but will not form coke.
The following statement exhibits, in a condensed form, the area and available capacity of the Colorado coal fields, based on the most reliable data obtainable. In making these estimates the economic limit of one- half mile from the general line of outcrop is assumed for highly inclined measures ; for measures dipping from 10° to 20° at from one to two miles, according to the amount of inclination away from the outcrop, and the thickness and quality of the coal. For horizontal or slightly inclined measures, four miles is assumed to be the working limit for
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HISTORY OF COLORADO.
thick coal, and three miles for beds from three to four feet thick only. An exception may be noted in the case of the upturned measures of the Great Hogback, where the enormous thickness of superior coal, the depths of the gorges, or points of attack, below the mean level of the outcrop, and general accessibility, makes it reasonable to assume that the seams will be worked to an average distance of one mile. In the Raton field, which has been carefully meandered, the small areas in advanced position, relative to the points of attack, have been calculated and added to the total. Owing to want of accurate data it was impos- sible to do this in the case of any other field. The least workable thick- ness is assumed to be three feet, for although smaller seams are worked even now under very favorable conditions, they cannot be followed with profit beyond a short distance.
The above limits may appear to many engineers much too circum- scribed, even when measured by European standards of the present day without taking into account the more advanced engineering methods of the future. But we cannot anticipate the possibilities of the latter; neither would it be reasonable to apply the former under the conditions existing in this country. Moreover, on the same ground, we might object to the estimates made on other coal fields. On the whole the figures here given are thought to possess a comparative value, though there can be no doubt that they will be considerably modified by the results of future surveys.
ESTIMATED AREA OF COLORADO COAL FIELDS.
Grand River Field (Colorado portion).
SQUARE MILES.
Yampa Field, including part of Wyoming Field in Routt County 6,950
La Plata Field (Colorado portion) 1,100
Raton Field (Colorado portion) 1,250
Northern Colorado Field 6,800
1,300
North Park Field. 300
South Park, Canon City, and Tongue Mesa Districts 100
Dakota Measures (Southwestern Colorado) 300
Total
18,100
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HISTORY OF COLORADO.
ESTIMATED QUANTITY OF AVAILABLE COAL, IN COLORADO FIELDS.
LOCATION.
ACCESSIBLE AREA IN SQUARE MILES.
Grand River Field (in Colorado)
1,116
AVAILABLE GROSS TONNAGE. 26,384,800,000
Yampa Field.
440
5,961,500,000
La Plata Field (in Colorado)
300
3,387,200,000
Raton Field (in Colorado)
473
4,490,200,000
Northern Colorado Field
405
2,568,600,000
North Park Field
80
1,806,500,000
Cañon City, South Park, and Tongue Mesa Districts
49
429,000,000
Dakota Cretaceous Measures
50
169,300,000
Total
2,913
45,197,100,000
Total net tonnage, or 75 per cent. of gross estimate
33,897,800,000
It will be interesting to compare the above figures with the estimate of Dr. H. M. Chance, on the available bituminous coal of Pennsylvania. The total area of coal land is calculated at something less than 9,500 square miles, which includes 470+ square miles in the anthracite fields. No reliable estimate has yet been made of the amount of available anthracite.
The net available bituminous coal is placed at 22,908,000,000 long tons,-equal to 25,657,000,000 short tons,-the limiting thickness being three feet, and the maximum distance from the outcrop two miles where the beds are not less than four feet thick. The distance limit, it will be seen, corresponds to the maximum assumed for beds, inclined from 10° to 20° in Colorado, where, in most of the accessible measures, the tendency is to flatten out away from the outcrop. In Pennsylvania the working limit is largely determined by the depth below water level; but in the dry Colorado climate, with extensive areas of slightly inclined measures elevated above the surrounding country, and to some extent drained of surface water, the working limit will in most cases be determined rather by the cost of mine haulage; consequently, where coal has been assumed as accessible, at a distance of four miles from the outcrop, it is obvious that, under the circumstances, it will be made available before the fields are exhausted.
The available bituminous coal of Alabama has been estimated by Mr. Henry McCalley at 108,394,000,000 tons in the seams over eighteen
1
.
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HISTORY OF COLORADO.
inches thick. Evidently there is a vast amount of coal in Alabama, but the assumed limited thickness is so small that no fair comparison can be made between Mr. McCalley's estimates and those given for Colorado and Pennsylvania. The States which rank Colorado in area of coal land are, according to Ashburner : Illinois, with 36,800 square miles, and Missouri with 26,887 square miles ; while Iowa, Kansas and West Virginia are not far behind, having 18,000, 17,000 and 16,000 square miles respect- ively. In all these States, except West Virginia, the coals are of inferior quality when compared with our own.
With the composition of Colorado coals, and the causes operating to produce the several varieties, we shall not now attempt to deal ; such subjects can only be discussed intelligently from a purely scientific stand- point. The foregoing brief review of our coal fields, is merely intended to give the reader a general idea of the magnitude of our resources in that direction.
Conclusions naturally suggest themselves. The vast reserves of fuel will play a more important part in the future prosperity of the State than all our metalliferous deposits combined ; for the supply is practically inexhaustible, and the market a large and growing one.
The physical conditions attending the close of the Marine Creta- ceous and the opening of the Laramie, foreshadowed the great conti- nental revolution, which permanently elevated the Rocky Mountain region and adjacent plains country above the ocean level.
During the early part of the Laramie, especially west of the conti- nental divide, we find marine conditions to have alternated with brackish- water conditions. There were times when extensive swamps and marshes stretched away, probably a hundred miles, from the permanent shore- lines. There were also intermediate periods when the conditions were favorable to the existence of a purely marine fauna, and so we find beds containing coal, and the remains of land vegetation, interstratified with others containing marine shells; indicating that the land was subject to oscillations of level, and occasional incursions of the ocean. In the higher horizons of the Laramie, evidence of these alternating conditions
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HISTORY OF COLORADO.
no longer exists, and the organic remains are of typical land, or brackish- water forms.
Several hundred species of fossil plants, indicating the luxuriant vegetation of this epoch, have been collected in Colorado localities, notably in the Raton Mountains, at Rouse, in the Boulder County districts, at Golden, in the vicinity of Crested Butte, and on Crystal River. The Denver beds, overlying the coal-measures, are rich in species, referred by Newberry to the upper part of this epoch.
Most of the Laramie genera have their representatives on this con- tinent at the present day ; but certain types like the Fig, Magnolia, Cinnamon, Fan-Palm, etc., common in Laramie beds, indicate a warmer climate than now exists ; a difference that may be attributed to the low- ering of temperature consequent on the elevation of the land.
The vertebrate life of the epoch included chiefly reptiles. The Dinosaurs, regarded as characteristic of the Mesozoic, are still dominant, but in diminishing numbers and highly specialized forms. A genus of huge horned Dinosaur, the Ceratops, existed all along the Rocky Mountains, several individuals having been found in the Denver beds which for this reason are regarded by Marsh as probably of Laramie age, although this question has not yet been definitely settled.
Mammalian life appears to have been mainly restricted to small marsupials, of which quite a number of species have recently been described by Marsh, from what are considered to be Laramie beds of Wyoming. This is the first discovery of abundant mammalian remains in Cretaceous strata, although similar types were already known from the Jurassic of Colorado.
In their affinities nearly all these Laramie forms were allied to their earlier representatives, and in nowise foreshadowed the highly organized true mammals, which suddenly appeared in vast numbers at the beginning of the Tertiary.
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HISTORY OF COLORADO.
CHAPTER III.
CENOZOIC ERA-THE TERTIARY PERIOD-GREAT FRESH-WATER LAKES OF THE TER- TIARY-EOCENE EPOCH, STAGES AND LIFE-DISTURBANCES AT THE CLOSE OF THE EOCENE-OLIGOCENE OF THE FLORISSANT BASIN-MIOCENE EPOCH, STAGES AND LIFE-END OF THE CONTINENTAL REVOLUTION-PLIOCENE EPOCH AND LIFE- TOTAL ELEVATION OF THE LAND-QUATERNARY PERIOD-THE EPOCHS REPRE- SENTED IN COLORADO-LIFE OF THE QUATERNARY-POSSIBLE EXISTENCE OF MAN IN COLORADO DURING THIS PERIOD-EVOLUTION OF LIFE THROUGH THE CENO- ZOIC ERA-ERUPTIVE ROCKS AND PAST IGNEOUS ACTIVITY-ORE-DEPOSITS OF COLORADO-CONDITIONS GOVERNING THE FORMATION OF ORE-BODIES-THEORET- ICAL CONSIDERATIONS-GEOLOGY OF SOME COLORADO MINING DISTRICTS-IRON ORES-OIL-SHALES AND MARBLE-MINERALS-CONCLUDING REMARKS.
CENOZOIC ERA.
This is the third grand division of geological time as applied to the development of life, although the fourth in geological history. The Cen- ozoic is divided into two periods, viz., the Tertiary and Quaternary. The first finds remarkable representation in the fresh-water lake-beds of the West, which have yielded so abundantly of well preserved mamma- lian remains, and thus enabled palæontologists to trace, step by step, the ancestry of many existing species. The Quaternary beds are also well represented, but have not yet been studied in detail.
The elevation of the interior part of the continent was brought about by successive stages of upheaval, beginning at the opening of the Laramie, and terminating at the close of the Tertiary. The first eleva- tion ceased when the bed of the inter-continental sea had about risen to tide-level. By the second upheaval, at the close of the Laramie, the entire region lying east of the Wahsatch, and west of Middle Kansas and Nebraska, was finally elevated beyond the reach of ocean waters.
65
HISTORY OF COLORADO.
The dynamic movement accompanying the second stage of conti- nental upheaval, produced a certain amount of folding parallel with the axes of the Wahsatch and Rocky Mountain Ranges. In the region between these ranges broad areas were depressed, and became the basins of three immense fresh-water lakes. These basins have been called, respectively, Green River, Uinta and San Juan. The first was confined to the country north of the Uinta uplift ; the second covered North- western Colorado, and a large part of Eastern Utah; while the third covered the southwestern corner of Colorado, and extended into New Mexico. During the early Tertiary the lakes of the San Juan and Uinta basins may have formed a continuous sheet of water ; or, as gen- erally supposed, the former was merely an extension of the latter during the Lower Eocene Epoch. A fourth, but smaller lake occupied a basin lying between the Sangre de Cristo and the southern continuation of the Wet Mountains. The last is known as the Huerfano basin.
Throughout the epoch of the Lower Tertiary (Eocene) there was a steady accumulation of sediments, in the Green River and Uinta basins, until the deposits attained a thickness of 10,000 feet. In the Huerfano basin sedimentation probably ceased at the end of the Middle Eocene, and in the San Juan basin at the end of the Lower Eocene.
While sedimentation appears to have continued almost without interruption through the Lower Tertiary, it is obvious that great cli- matic changes must have taken place, to have so thoroughly individualized the groups or stages, which it includes ; for not only are these each litho- logically distinct from the others, but there is in each case a marked dif- ference in the character of the vertebrate remains,-so much so, that the latter can usually be relied on to determine the relative age of the beds.
The several groups which have been shown to possess distinct lithological and faunal characters, are known, respectively, as the Wahsatch, Green River, Bridger and Uinta. The two last find but meager representation in Colorado, but the former, which are the oldest, cover large areas in the western part of the State, being well exposed along the White, Grand and San Juan Rivers.
5 II.
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HISTORY OF COLORADO.
Underlying the Wahsatch of Northwestern New Mexico, are dark- colored marly beds, about 500 feet thick, called by Cope the Puerco group, which are thought from the faunal remains to be still older than the Wahsatch stage.
The Wahsatch beds or lowest Eocene, consist of variegated clays, marls, shales and toward the base, sandstones. The Green River beds consist of highly bituminous shales and marly limestones, usually exhib- iting a very continuous, thin lamination, suggesting the name "Book Cliffs" to the extensive exposure of these beds on Grand River. Some of the Book Cliffs strata are so rich in condensible hydro-carbons as to yield up to thirty per cent, of dark brown oil on distillation; and the rock, when piled up and ignited, burns with a bright flame like poorer varieties of cannel coal. The well preserved fossil fishes, so commonly seen in the Denver curiosity stores, are from the beds of this group in Wyoming.
Bordering the Great Eocene lakes were dense forests, which afforded protection and subsistence for countless numbers of strange animals of types long since extinct. Some idea of the variety and abundance of mammalian life, in Colorado and the adjacent country, during this epoch, may be gained from the fact that the species already recognized, in the remains from the three basins just mentioned, must be double the number now existing on this continent. Many of the Eocene species were of gigantic size, and possessed of remarkable char- acters. Tapir-like forms appear to have predominated. Remains of the Coryphodon, a genus of Ungulates without specialized characters, and common in the Eocene of Europe, are common in the Wahsatch deposits of Colorado, but are entirely confined to this horizon, which has, in consequence, been designated by Marsh the, "Coryphodon beds." Remains of the earliest representatives of the Horse family, of the genus Eohippus, are also found in the same beds; while the remains of another genus, the Orohippus, more nearly allied to the modern Horse, are found in the Bridger beds of the Middle Eocene. Others of still more modern type, are found in higher members of the Tertiary, the
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HISTORY OF COLORADO.
approach to the modern form increasing as we ascend, until in the Qua- ternary the species all belong to the existing genus Equus. The evolu- tion of the Horse is one of the most interesting of the well-established facts that palæontology has given us,-facts which have had great influence in moulding the present accepted theory of the origin of species.
The Green River beds contain remains of fishes, plants, and insects but so far as known, none of mammals. The nature of the life, and the lithological composition of the Green River group, point to the presence of brackish-water in the middle and northern of the great Eocene basins during this stage; indicating that they had become so far depressed as to be connected with tide-water through the western outlet.
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