History of Delaware : 1609-1888, Part 2

Author: Scharf, J. Thomas (John Thomas), 1843-1898. cn
Publication date: 1888
Publisher: Philadelphia : L. J. Richards
Number of Pages: 776

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A narrow ridge of sand separates Rehoboth Bay and Indian River Bay from the Atlantic Ocean, while Indian River Inlet is a passage, torn by storms, through this ridge for the waters of the two hays to the ocean. This inlet rarely contains more than a few feet of water, and after a great easterly storm is elosed by sand washed into it from the ocean ; but soon the dammed up waters of the bays break again for themselves a passage to the ocean. These large bays have each a sur- face of twenty-five miles, but their depths rarely exceed four or tive feet. The most northerly of these bays is Rehoboth, which, nearly square in shape, extends parallel with the ocean, from which it is separated by the ridge. Line Creek, Middle Creek, Herring Creek and Guinea Creek empty into Rehoboth Bay. Long Neck, a narrow sand bar, separates these last-mentioned creeks from Indian River Bay, while the "Burtons '-marshy islands, ealled on old maps Station Islands-indicate the changes that have taken place in these waters. In- dian River Bay is about eight miles long and from two to four broad ; it fronts the Atlantic Ocean for three miles, and is separated only by the narrow ridge mentioned above. Millsboro' is on Indian River. Pepper Creek, Vine Creek and White Creek flow into Indian River.

Fresh Pond and Salt Pond are two ponds a few miles south of Indian River-the former is about half a mile in length and two hundred yards wide. and is from twenty-five to thirty feet deep. It has apparently no outlet or streams flowing into it, Delaware is an agricultural State; a part of it is in a high state of cultivation. Beside wheat, In- dian corn and other grain, peaches are grown in and contains but few fish. It is separated from the Atlantic by a ridge of sand not more than an eighth of a mile wide. The other, Salt Pond, is immense quantities and sent over the country: about the same size and situated about three miles emall fruits are also raised for transportation. In

Its water is salt, and even more so than that of the ocean.

Asawaman Bay is formed by Jefferson Creek, and is long and shaHow, about seven miles long and from one to one-half' a mile broad, and from three to five feet deep. It is separated from the Atlantic by Fenwick's Island, a long narrow cape and ridge of land which extends in length twenty- three miles.

The streams which flow into the Chesapeake Bay and take their rise in Delaware, are the Nan- ticoke, the Broad Creek and the Pokomoke. Sea- ford finds water communication with the Chesa- peake Bay down the Nanticoke. Portsville is reached by Broad Creek, and the Cypress Swamp is reached by the Pokomoke. Back Creek, the Bohemia and the Sas-afras, in New Castle County ; the Chester, the Choptank and the Marshy Hope, in Kent County ; and the Wicomico in Sussex, all take their ris- in the Sandy Ridge of Delaware and discharge their waters into the Chesapeake,- they all belong more properly to Maryland than to Delaware.

The lines of railroad in Delaware reach every locality and give the people every facility of transportation. The State has over three hun- dred miles of railroad, and the respective com- panies are treated more fully elsewhere in another chapter.

The waters of the Chesapeake and Delaware Bays are connected by the Cheapeake and Dela- ware Canal, navigable for coasting vessels and propeller steamers. This canal extends from Del- aware City, forty six miles below Philadelphia, to Chesapeake City, on Back Creek, a navigable branch of Elk River, in Maryland. The eanal is thirteen and a half miles in length, sixty-six feet wide at the top and ten feet deep. It has two tide and two left lift locks, and is located four miles through a deep cut ninety feet in depth; it was completed in 1828 at a cost of two million two hundred and fifty thousand dollars, and has since proven a source of incalculable value to the pro- ducers of the surrounding country in furnishing an outlet to the markets of the large cities.

A ship canal has been contemplated for many years between the two bays, for which a company was chartered by Maryland and by Delaware, and the line located from the Sassafras River to the Delaware Bay. Beyond securing the right of way nothing has been done. Falem Creek and the Delaware River have been connected by a canal.

HISTORY OF DELAWARE.

the northern part of the State are numerous manu-

The geology of the State of Delaware is com- factories. Wilmington is the principal centre of paratively simple. The oldest Archean rocks industry. New Castle, also, has important rolling- mills, and cotton and woollen factories. On Bran- dywine Creek are some of the finest flouring-mills in the United States, to which vessels drawing eight feet of water can come. The foreign trade of the State is effected chiefly through Philadelphia, Bal- timore and New York ; so that its direct foreigu trade is very inconsiderable. cover all that portion of the State which lies to the north of the Philadelphia, Wilmington and Baltimore Railroad, where they are tilted at high angles, contorted and overthrown The region is one of great interest, and offers to the field geolo- gist problem- of such moment as to make it a classie field in American geology Resting upon the eroded edges of the Azoie rocks are successive series of plastic clays, sand marls and green sands, of Cretaceous age, which form quite uniform strata CHAPTER II. dipping at a low angle to the southeast. This belt, having a width of about eighteen miles, ex- THE GEOLOGY OF DELAWARE.1 tends from the Archean hills to the latitude of Noxontown mill pond. just south of Middletown. The Cretaceous is succeeded by a stratum of white or lead colored clay having a thickness of ten to twenty feet.

DURING the year- 1837 and 1838, Prof. Jas. C. Booth, in accordance with an act of the State Legislature, made a geological survey of Delaware, the results of which were published in a report that appeared in 1841. This old memoir is of great value, both from the accuracy of the author's observations and his minute attention to detail; we eannot, therefore, expect to take anything from the character of this work, our aim being to so com- pletely reconstruct our geology as to bring it into sympathy with results in adjacent States.

The formation represent-d within the bounds of the State are Archean, Cretaceous, Tertiary and Quaternary. The relations and positions of the several divisions of these formations are represented in the accompanying table, also the thickness of each. It will be understood that the formation oldest in age and order of deposition is placed at the bottom.

AGE.

GENERAL SERIES

DELAWARE SERIES.

Quarternary or Modern.

Modern. Post Glacial. Glacial.

Bog Clay Alluvium,

Delaware Gravels-10-10'.

Pliocene.

Bine Clay-3-10' .. Glass Sand-40'.

Tertiary.

Miocene.

White Potter's Clay-10' -20%.

Eocene.

Upper.

Middle Mart Bed-139'.

Middle.

Inderate Mail Bed (Red Sand of New Jersey )-149'.

Cretaceous.

Lower.

L .wer Mari Bed-60'. Plastic Clays (Potomac Formation) -

Mira Schiste and Gneiss, with Erup- tive Gabbros and Gabbro-Durites.

Archean.

Magnesian Marble,

Quartzite.

1 Contributed by Prof. Frederick D. Chuster, of Delaware College

This continues as far south as Murderkill Creek, and from fossiliferous evidence is probably Miocene South of Murderkill Creek, the Miocene is suc- ceeded by three to ten feet of light or dark blue clay, beneath which is a uniform stratum of fine white glass sand of at least forty feet in thickness. That all the State south of Murderkill is later Pliocene rather than Modern, as the older writers have claimed, has, we think, been well demonstrated. All the beds of the Tertiary lie in a nearly hori- zontal position, dipping at a still lower angle than the Cretaceous, and probably unconformable to the same.

Covering all of the foregoing formations, and reaching up the flanks of the Azoie hills to the height of two hundred feet or more above tide is a layer of sand and gravel, which to the north is of a coarse red nature, and to the south is fine and white. These gravels are of Quaternary age. and have been styled by the author the Delaware Gravels and E-tuary Sands, respectively. Along the river and bay shores is also the belt of boz elay, which is modern, and of more recent origin than the Gravels.

THE ARCHEAN .- Generally speaking, the south- ern line of the Azoie or Archean rocks is the limit of the " highlands," but in certain places they extend well into more level regions. Beginning with a point upon the Maryland boundary, a little north of where the latter is cut by the Mason and Dixon line, the limit of the rocks runs in a north- east direction, cutting through the western end of Newark, and following the northern boundary of the town. Thence it runs close to the south shore of White Clay Creek to a distance of two miles beyond Roseville, where it makes an abrupt bend to the north, until at Stanton the rocks cease to be found. A mile back of the railway station, they again appear, continuing to a point about a mile back of Newport, where their course runs slightly

THE GEOLOGY OF DELAWARE.

to the southeast, crossing the Wilmington turn- the hypersthene rock passes into a nearly pure pike just before it is intersected by the Wilmington bornblende feldspar rock, which from it- schisto- Northern Railroad ; thence it follows the turnpike or banded structure make- it a hornblende gneiss. through the southern half of the city, when it turns abruptly south to the river. In the same way it is found that the true gabbros occur in all stages of transition into rocks distinct- The character of the country covered by the ly granitie in character, or more nearly like many Archean rocks is distinctly hilly, and stands in of the European norites or the trap granulites of Saxony.

strong contrast to the low-lying region to the south. The rocks, however, are too uniform in texture and structure to cause marked topographie outlines. The region is rather rolling, or the hills low and undulating, between which are corres- ponding bowl shaped depressions. The elevation of this highland region varies between two hundred and three hundred and fitty feet above tide, gra- dually increasing to the north.

The Archean area of the State can be divided into two nearly equal areas. First, a southern club- shaped area of eruptive gabbros and hyperites with associated amphibole rocks, and Second, an upper elliptical area of softer micaceous gneisses and schists.

Almost the whole of Brandywine Hundred, and the southern half of Christiana Hundred are eov- ered by the rocks of the first class. To the west of flatten and elongate certain of the mineral con-

Brandywine Springs these rocks, however, taper out into a narrow helt of not over a quarter of a mile in width, which runs along the southern limit of the Archean to beyond Newark.

Another interesting development of the same rocks oceurs to the southwest of Red Mills, and thence to the well-known elevations called Iron and Chestnut Hills. The typical hyper thenie gabbro or hyperite of the club-shaped area just described is represented by the so-called " Brandy- wine granite," which is quarried to such an exten- sive degree in the neighborhood of Wilmington. It is a rock of dark bluish gray or bluish black color of great hardness and firmness, and is without doubt one of the most valuable and durable stones in existence.1

This rock has been studied in detail by the writer, and from its wide variation in composition and structural characters is of peculiar interest. The rock, as studied under the microscope, is found to consist of a granular mixture of hypersthene, diullage plagioclase feldspar ( labradorite ), with ae- cessory quartz, biotite hornblende, magnetite, pyrite und apatite.

The most remarkable fact observed in the study of these rocks is the intimate association of highly schistose black hornblende rock with these massive gray gabbros. The black hornblende rock is, after past mieroscopie studies, found to be but an ex- treme stage of variation affecting to a greater or less degree the whole gabbro mass. Ilornblende, which is the true gabbro is but a rare or accessory constituent, is found to increase in amount until

1 Bulletin, No. 41, U. S. Geological Survey, Washington.

The massive gabbros, best exposed in the exten- sive quarries of Brandywine Hundred, are entirely massive in structure, or with an entire absence of those planes of bedding which characterize sedi- mentary deposits. All evidence obtained in the field and with the microscope confirms the belief that they are truly eruptive, and that the rock was at one time in a more or less molten -tate, in which condition it was probably forced up through the older mica schists which lie to the north and which also lie buried to the south beneath younger clays of the cretaceous. The banded or schisto-e structure prevalent in the associated hornblende rocks proves also that the rocks of this gabbro belt have been subjected to great pressure, a pre-sure which the microscope shows was great enough to stituents of the rock and to erush others into frag- ments.

To the north of the area of gabbros and horn- blende. rocks, and resting upon the latter, is an extensive formation of highly micaceous slaty rocks. so easily friable as to erumble to the touch, and which break into a loose sandy loam of great rich- ness.

The rocks of the mica schist belt are all strati- fied with variations of bedding, from that as thin as slate, in the mien schists, to that of a heavily bedded character in more highly metamorphosed forms. Both strike and dip in these rocks are subject to great variation. Variations of strike in this case proving that the elevating force acted very unequally, showing itself in a twisting and undu- lation of the out-cropping edges of the rock. Va- riations of dip enabling the geologist, by plotting upon paper those observed along any line of see- tion, to show that the micaceous rocks of Delaware have been pressed into a series of folds or waves. like the wrinkle- in a piece of cloth, by an enor- mous lateral pressure, a pressure which resulted in the elevation of the Blue Ridge from New Eng- land to Alabama, of which uplift the crystalline rocks of Delaware form a part.

The mica schists and gneisses of Delaware form a continuation of the so-called Philadelphia Gneiss helt, which covers the greater part of Delaware County, and the southern portion of Montgomery, Bucks and Che-ter Counties in Pennsylvania.

These rocks have been the subject of much con- troversy, and their age is still undecided. By many they are regarded as altered Palaezoic sedi-

HISTORY OF DELAWARE.

ments, while others continue to regard them as of Archean age. This latter designation is based upon their lithological similarity to many of the older crystalline schists, They have hence been referred to the White Mountain, or the Rocky Mountain series, one of the upper members of the Archean.

Associated with the softer slaty miesceons rocks are probably intrusive masses of coarse grained granite, which vary in thickness for several inches up to many feet. These granites often become so highly feld-pathic as to possess considerable economic value, inasmuch as the feldspar fre- quently becomes decomposed into Kaolin.

The celebrated deposits around Hockessin are of this character. Dixon's quarry near Wilming- ton has produced very fine yields of felispar. 1 very notable vein cuts across the road leading up the Brandywine, about one and a half miles from the head of the State. Its width is about twenty feet, and the material a mixture of red orthoclase albite, blue quartz and muscovite. The rock is quarried for the valuable feldspar, used in the manufacture of artificial teeth.

Quartites are also imbedded with the mica schists name of flint. At Tweed's Mill, above Newark, this roek is ground into a fine flour, when it is shipped for use in the manufacture of porcelain ware.

It is an interesting point to note that these quartz veins are frequently of a cellular character, when they are quite similar to many gold bearing veins in rocks of like are in Virginia, North Caro- lina and Georgia. Hence it is not at all improb- able to suppose that gold bearing veins may some day be discovered upon the farms of Northern Delaware.

Another common associate of the mica schists is a black hornblende rock interbedded with the latter. and forming masses often several hundred feet in thickness. In places, this alternation of hornblende and micaceous rocks is frequent. .

THE CRETACEOUS,-The cretaceous of Delaware, a continuation of the same formation as developed in New Jersey, extends across the state as a north- east and southwest belt, with a breadth of eighteen, and a length of from fifteen to twenty miles. The northern limit of the belt has already been traced out as making the southern boundary of the Archean. The southern limit was a little to the south of, and parallel with, Appoquiniminh Creek, cutting through the centre of Noxontown mill- pond, and thence proceeds in a straight south- westernly direction. The different subdivisions of the eretaceous form uniform beds dipping at a low angle to the southeast. This dip was carefully measured at the deep eut, along the Chesapeake and Delaware canal, and found to be at this point at the rate of forty-five feet to the mile.

These subdivisions will be noticed in the chrono- losical table at the opening of this article and will be described in order.

THE PLASTIC CLAYS-This formation is the thickest member of the cretaceous whose northern limit corresponds with the upper border of the cretaceous. Its southern line begins a few miles south of New Castle, and extends in a southwest- ernly direction to just below Red Lion, crossing the railroad betwen Porter's and Kirkwood, and cutting the State line about two miles north of Chesapeake City.

Although of so much importance, it is, owing to the great thickness of the overlying gravels, rarely exposed, and even when more favorable opportuni- ties are offered. but a few feet of the characteristic Red Clay appear above the surface.

The clay is more generally red and highly plastic; in other cases it is mottled, and again white and sandy like fire elays.

The best exposures are along the lower levels of the gullies cut by the ereeks of upper New Castle County, particularly along Red Lion Creek. Oc- casionally the characteristic red clay comes to the surface at points along the roads. The hills to the and when pure and white are worked under the east and north of Christiana are formed of these elase, which outerop very frequently along the road leading from Christiana to New Castle.

Judging from the many points where we have found this elay exposed we are convinced that it has an important economic value for the manufacture of terra cotta ware. The supply is practically inexhaustible, and the clay is to all appearance as good as similar clays worked in New Jersey for manufacture into terra cotta ware.

The plastie clays of Delaware have within the past year been correlated with the so-called Potomac formation of Maryland and Virginia, and have important relations to certain older gravel deposits which will be dwelt upon later.

SAND MARIL .- This is a deposit of a loamy yellow siliceous sand, with which is mixed some green sand (marl), whose thickne -- is about ninety feet. It rests upon the plastic clay formation, and covers that part of New Castle County, lying he- tween the southern limit of the plastie elays, and the eanal.

THE MARL BEDS .- The marl beds cover a com- paratively small area in the State, and are prac- tieally limited to that division of New Castle county called St. George's Hundred.

The first important outerops of green sand oeeur along the Delaware and Chesapeake Canal, the channel of which ents deeply into the formation. Its northern limit, as determined by old mart pits, runs approximately parallel with the canal, keeping a distance of from a quarter of a mile, to a mile. From this line the marl extends south- ward to another boun lary parallel with, and about

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THE GEOLOGY OF DELAWARE.

one mile south of Appoquinimink Creek, where it is divided into three very distant layers. (1) A gives place to the tertiary clays. lowermost pure green sand covering most of the

The divisions of the green sand formation are belt, and well-exposed along Drawyer's Creek and found, with two exceptions, to correspond with those made by the New Jersey Survey, The chro- nological table at the opening of this article gives the subdivisions of the marl beds.

LOWER MARL BED .- This stratum, which ex- tends as a narrow belt on each side of the canal, is found to outerop along the entire length of the same, rising about a foot above the surface of the water, and farther west to the height of twenty tret. The lowest layer in this deposit is a tough blueish black marl, which, upon drying, turns to a lighter, ashen or earthy color, when it is found to be made of a mixture of green sand, siliceous sand and argillaceous matter. The solid particles are coated with chalky carbonate of lime, which, under the microscope, appears as a fine white powder of a granular character.

Overlying this last layer is a shelly layer of about three feet in thickness, and containing the characteristic fossils of the Lower Marl Bed of New Jersey.

Above this laver, which we have called the "Black Argillo-micaceous Marl," to the west of the Delaware railroad, it is exposed in the " Deep Cut," where its characters can be well studied. This black marl is composed of minute sharp gla-sy partieles of quartz, coated with a gravi-h dust, and associated with a few green sand particles of unu- sual firmness, together with a considerable quantity of minute scales of muscovite mica.

INDURATED MARL BED .- The northern limit of this belt, which is also the southern limit of the lower marl bed, starts near the mouth of Scott's run, and thence keeps parallel with the canal to the railroad, where it begins slightly to diverge, cutting the headwaters of the northern branch of the Bohemia river. The southern limit of the belt can only be approximately outlined, but as can best be determined, runs from Port Penn through the headwaters of Drawver's Creek, and crosses the Maryland line four miles below the head of Bohemia River. The deposit is divided into two layers : 1st, Lower layer of reddish siliceous sand, with some green sand, which occupies the upper border of the belt a little south of the canal ; and 2d, An upper layer of partly decomposed or indu- rated marl, of a rusty green color when dry, which underlies most of the area of the belt.

THE MIDDLE MARL BED .- This belt erosses the State with a uniform breadth of three and a half miles, the northern line running from Port Penn, a little north of Drawyer's Creek, and crossing the State line four miles south of the Bohemia River. The southern line crosses the center of the Noxon- town mill-pond, keeping parallel with and a little south of Appoquinimink Creek. The middle marl

Silver Run. (2) An intermediate laver of friable shells, from three to ten feet, exposed at the head of Noxontown mill-pond and along the south side of Appoquinimink Creek. (3) An upper yellow or reddish-yellow sand, occupying the southern verre of the belt.

THE ECONOMIC VALUE OF THE MARL .- The area covered by the marl beds has already been set forth with sufficient exactness to enable one to know where marl can be found. The supply within the area, underlaid by it, is probably inex- haustible. Its value as a fertilizer makes it wor- thy of consideration. Green sand is composed of grains of the mineral glanconite, mixed with greater or less quantities of impurities, as clay, siliceous sand, and mineral particles.

Glauconite is a compound of silica, iron, prot- oxide and potash ; the quantity of potash ranging from four to twelve per cent. Many of the New Jer- sey green sand marls contain from one to two and a half per cent. of phosphoric acid, and there is no reason to doubt but that the Delaware marls. which are geologically identical with those of New Jersey, may be equally rich in this last substance. When used, liberal dressings of the land should be made before plowing, in this way a large amount of potash is introduced into the soil, which, while at first insoluble, or not directly available, becomes slowly set free by decomposition, and renders it available to plants.

The effects of the marl are, therefore, lasting, and when applied every few years permanent. A careful inquiry into the results obtained from the application of marl upon some of the Delaware farms has convinced the writer that good results can be reached by its use. As a direct and imme- diate source of potash, green sand is not to be compared, by the rule of commercial valuation, with the easily soluble kainit; but as an easily available and cheap material for the culture and permanent improvement of land, green sand marl is a material worthy of the attention of those far- mers of the State whose lands are underlaid by it.

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History of Delaware : 1609-1888, Part 2

Author: Scharf, J. Thomas (John Thomas), 1843-1898. cn Publication date: 1888 Publisher: Philadelphia : L. J. Richards Number of Pages: 776

Author: Scharf, J. Thomas (John Thomas), 1843-1898. cn
Publication date: 1888
Publisher: Philadelphia : L. J. Richards
Number of Pages: 776