LIMDSTONEB * Lehigh County is well provided with limestones belonging to the Cambrian and Ordovician periods. The limestone strata ,aggregate about 4,000 feet in thickness. .They are fairly well distributed in that all except the five most northerly townships contain limestones; a few of the central ones contain only limestones as the outcropping strata. The limestones lie within the Great Valley, which cuts across the * county and contains most of the towns-Allentown, Catasauqua, West Bethlehem, Fountain Hill, Coplay, Cementon, Egypt, Ormrod, Fogels- ville, Alburtis, Maeungie, and Emmaus. Saucon Valley, part of which lies within Lehigh County, is floored with limestones. This is an off- shoot from the Great Valley. Limestones are exposed also along Hosensack Creek in Lower Milford Township. Table of limestones of Lehigh Comtg Thickness Ordovician in feet Martinsburg shales and slates overlying the limestones. Jacksonburg low-magnesian argillaceous limest.one used in portland cement m,anufacture . 6010-c B.eekmantown limestone composed of alternating high- and low-magnesian beds . IO~O~O~+- Cambrian Conococheague (Allentown) Tom&own dolomitic limestc Hardyston sandstone and ql Description Torn&own. limestone.-Tht: contains tne olaest limestones of the county. In general they are present only along the southern margin of the limestone valley, where they overlie the Hardyst.on sandstone. Due to complex folding and faulting the dis- tribution is not always normal. The position of the outcropping Toms- town strata near the base of the mountains bounding the Great Valley on the south is not Favorable for exposures as the talus from the moun- tain slopes conceals the edges of these strata. The Tomstown forma- tion consists of massive, hard, dolomitic and siliceous limestones inter- bedded with shaly layers containing practically no calcium carbonate. The Tomstown limestones have been utilized for blast furnace flux and for crushed stone. Allentown limestone.-Overlying the Tomstown and ,at places differ- entiated from it with difficullty is the Allentown formation. This is the most widespread formation of the county and occupies most of the s,outhern half of the limestone valley. It consists of thick to thin magnesian limestones, in which alternating beds differ greatly in their content of mfagnesia and silica. On a weathered surface exposing * Note: A mire complete discussion is contained in the writer’s volume “Limestones of Pennsylvania,” published by this Survey in 1934 as Bulletin M 20. That report is still available. 367 3G8 LEHIGH COUNTY different beds thirs variation in the amount of magnesia results in the formation of a banded structure that can be readily distinguished at a considerable distance. On weathering those beds with the greater amount of m,agnesia become much whiter than those with small per- centages. These limestonea have been quarried in many places for lime burning, for furnace flux, building stone, and crushed stone. Beekmantown lGmestone.-The Beekmantown limestones generally occupy the greater portion of the northern half of the limestone val- ley. They consist of interlbedded low- and high-magnesian limestonels. Some beds are sufficiently low in magnesia to be used in portland cement manufacture, although the interbedded high magnesian stone renders it difficult to avoid a mixture. These limestones have been used mainly for lime burning, for flux, for crushed stone and for building purposes and to a minor extent for cement manufacture. Jackso&urg limestone.-The most impure limestones of the county and yet the most valuable constitute the Jacksonburg f’ormation. These are discussNedunder Cement. The limeston.es of Lsehigh County, exclusive of the argillaceous variety described under C,ement, are widespread and have been quarried in Scores of places. It is .only a slight exaggeration to say th.at a qu#arry h’as been opened on every farm in the limestone areas. Th,e limestones of the county have been used for building purpose,s (described under Building Stones), for the manufacture of lime, for flux, and for cru,shed stone. The earlieslt use was for building stone and for lime. The first settlers opened small qufarries where they got stone for their own use to burn lime for m,ortar or for fertilizing the soil. Those farmers without limestone .on their ‘own property sometimes haul’ed the stone from their neighbors’ farms and burned it in small kilns ne,ar their residences. When the ir:on mines wer’e opened in the region and furnaces were erected there was a dem,and for fluxing st’one, and several quarries of considenable size were operat.ed for thiw purpose. With the advent of portland cement and the construction of ‘concrete roads, bridges, and buildings, the d’emand f’or cru,shed stone for aggregate developed. Each of these uses has followed more or less in t,he order named and at the present time crushed stone is the mos’t important. S’ome quarries have at different timeis been worked for each of the uses men- tioned but seldom f’or more than one at the same time. HIGH- AND LOW-MAGNESIAN LIMESTONES Inasmuch as the amount of magnesia present in the limestones ren- ders them either fit or unfit for specific purposes it is useful to have a quick method of roughly determining the composition wilthout a chemical analysis. LIMESTONE USES 369 The distinctions between high- and low-magnesia limestones, which are important in field exlaminations and find application in the study of th,e Tomstown, Allentown and Beekmantown formations of Lehigh County, have been described by the author in a previous public,ation.“4 The low-magnesia limestones are soft and easily bIroken in compari- son with the highly dolomitic ones, so thlat a geologist can with prac- tice rather closlely approximate the magnesian content by the hardness and toughness of the stone when struck with the hammer. The dolomi- tic stones are also finer grained and more compact than the less mag- nesi’an ones of the same region. High- and low-m!agnesia limestones can readily be distinguished on weathered surf,aces. The high-magnesia limestones contain numerous straight cracks running in all directions, along which vein material has c,ommonly been deposited in layers so extremely thin that the freshly broken surface scarcely indicates their existence. On being exposed to the we’athering agents these cracks fulrnish access to dis- solving fluids and the we(athered surface of the rock looks as though someone had hacked the stone with a steel cutting implement. Where high- and low-magnesia limestones are interbedded, the contrast on weathered surfaces is striking. The dol,omitic limestones likewise have many more gash veins of quartz and calcite than do the purer limestones. Thebre is ‘also a greater amount of quartz in the vein fillings of the dolomites. LimestoNes for liwee.-More limestone quarries in Lehigh County have been opened to get stone for burning th’an f,or any .other pur- pose. Most of them are small and are now filled with rubbish and the kilns nearby are in ruins. Almost every clump of trees in the fields c.onc8e,alsone of these abandoned qttarries. Of course, many of the quarries were opened .al’ong the #stream bluffs. Years ago it was the common practice for the farmers .to quarry and burn the sto.ne during seasons when there was little work t,o b’e don’e in the fields. The kilns were constructe,d of field stone,s, many ,of glaei,al origin, and wo’od was used floor fuel. The burning was n.ot very efficient and the limed fields now contain pi#ece,sof chalky-white, partially-burned stone that may have lain there for many decades. ,Students have been puzzled by these limestone fragments, so unlike the other limestones in appear- ance. Th,e farmers felt that it was profitable to add lime to the soil every thre#e to five years and by a definite program one-third to .one- :’ fifth of the farm would be limed each year. 3r Although the great bulk of the lime produced w,a,s use.d for im- proving the s,oils, at all periods the lime ne,eded to supply the local demand for m’ort,ar a1s.ocame from the:se same kilns. Gradeally the belief in the necessity of liming soils waned as fuel becam’e scarcer and labor more expensive, and the f,armers ‘ceased to manufacture their own lime. In a few well-favored places larger kiln’s we’re erected, coal was shipped in for fuel, and larger produ.ction resulted. Th’e pro,duct was sold f.or several miles about ,and ‘even ‘shipped considerable dista,nces. As it came into compe.tition with 84Miller, B. L., Limestones of Pennsylvania: Pennsylvania Topog. and Geol. Survey Bull. M 20, p. 11, 1934. 370 LEHIGH COil?TP lime produced in other sections, more care was taken in its manufac- ture, both in the selection Iof the stone and in the burning. The early product. naturally was of variable quality. The farmer burned whatever stone he .had on his property. Some of the Toms- teown limestones are high in silica and alumina and almost all others are highly magnesian. Lime is not produced commercially at present in Lehigh County. Hlowever, from time to time some old kiln is restored and a small quantity of stone burned for local use. Formerly there were many fairly large lime plants in the east, south, and southwest parts of Allentown, at Limeport, and in the vicinity of Catasauqua. Most of the quarries furnishing the stone are now idle or are being worked for crushed st,one. There are few places in the county where the highest grade of lime could be produced.