GEOLOGY.1

Lancaster County presents three prominent geological features, which it may be well to notice separately, Commencing on the northern boundary, the Conewago range of hills separating the county from Dauphin and Lebanon Counties, belongs to the Mesozoic red sand stone period. The shales and gravelly soil of this formation spread southward. A glance at Scott's County Map, will show the range of hills commencing at Bainbridge, on the Susquehanna, extending in a line curving northwardly, then southeastwardly, with a general eastward course, embracing the greater portion of surface of the northern tier of townships. The limestone valley, constituting the central portion of the county, extends by a narrow inlet between two Gravel hills, in Penn township, not over a mile apart, (southeast of Manheim,) which opens into a limestone basin, around the borough of Manheim, widening out and embracing a large portion of Penn, Warwick, Clay and Ephrata townships, and portions of West and East Cocalico. The red shale or gravel formation east of Reamstown, and on the south-eastern side of the Cocalico creek, and north of the Conestoga creek, in a narrow strip, extends westward, crossing the southern portions of Ephrata, Warwick and Penn townships, to the aforenamed inlet. The Reading and Columbia Railroad passes nearly through the centre of this isolated valley. This Mesozoic red sand stone, is a portion of what Dana calls the Palisade range, which extends from Rockland, on the Hudson river, southward through New Jersey, Pennsylvania and Virginia, east of the Blue Ridge, in a continuous line of about 350 miles in length. It crosses the Delaware between Trenton and Kintnerville; the Schuylkill about 12 miles below Reading, and the Susquehanna river between Highspire in Dauphin, and Bainbridge in Lancaster county. In York county this belt inclines southward, in conformity with the Appalachian flexures, or mountain ranges on the N. W.

The Mesozoic or Medieval time in the Earth's history comprises a single age only— the Reptilian. It is remarkable, however, that very few fossils or signs of life of any kind are found within the county. The rock is in general a red sand-stone, passing into a shale or conglomerate, and occasionally including beds of impure lime-stone. The brown building stone, often called freestone, used in the erection of our County Jail and Court House, were quarried in the Black Oak Ridge, in Clay Township. Other quarries of sandstone are opened along the range of hills. Millstones are also made from a hard millstone grit found in Cocalico Township, and other points. Extensive dikes of trap or greenstone are met with in the Conewago hills, as also below Bainbridge near Millersville, and crossing thence towards Safe Harbor and at various other points. This Trap rock is of igneous origin, and belongs to the class of rocks met with in volcanic countries, like lava, being in fact the melted material of older rocks, ejected through fissures in the sand stone. In some places the sandstone is baked into a hard grit by the heat, and at times blown up by steam so as to seem scoriaceous, or the clayey sandstone is changed into very hard rock, similar to Trap itself. Minerals like the epidote and tourmaline result from this baking. The predominant red color in the soil, arises from the oxidation of magnetic iron grains present in it.

The calcareous formation, or the Limestone Valley, extends from the Gravel Hills, or Red Sandstone formation, to the Gneiss and Talc Slate Hills, commencing at Safe Harbor east of the Conestoga creek, inclining towards Willowstreet, thence eastward below or south of Strasburg, in a westwardly course along the boundary between Salisbury and Sadsbury Townships. This Limestone Valley as well as the Gneissic portions, belong to an age or period prior to the shales. The Palæozoic age is represented by a hard quartzite named the Postdam sandstone by the geologists of New York, a rock which is remarkably compact and rather fine grained, and consists almost exclusively

1 Drawn up by Mr. J. Stauffer, Lancaster.

of nearly pure silicious sand. It rises in a bold ridge ending in a precipitous cliff at Chicques on the Susquehanna, a mile and a half above Columbia. This formation extends eastward from the river towards Rohrerstown and between Silver Spring and Mountville. It also appears between Lancaster and Neffsville, and in the eastern portion of the county, on Laurel Hill, extending into Berks County. The Hill in the extreme northeastern corner of the county is also an upheaval of this peculiar formation and corresponds with the South Mountain in Berks County, being the lowest in the Palæozoic period. From the Chestnut Hill Ore Banks many thousand tons of Iron Ore (argillaceous oxide and hematite) have been taken from the overlying clay. Numerous other localities exist throughout the county, where Iron Ore is found, commonly along the borders of the Limestone formation. The curious calcareous rock, called Potomac Marble, (Breccia) occurs north of Manheim and east of Bainbridge. Argillite (or clay slate or roofing slate) is found at Peach Bottom, on both sides of the river and inferior qualities occur in Rapho and Penn Townships, but the laminated structure is found defective to a great degree.

Considering the extent of the Limestone Valley, between the gneiss and red sand stones, and that in the opinion of geologists most limestone was formed from the calcareous relics of living species accumulated in oceanic waters, like the coral limestone of the present period, and partially protected by barriers from the incursion of detritus, it is probable, therefore, that this valley was once an arm or bay of the Atlantic Ocean, and now constituting the most valuable and fertile portion of the county for agricultural purposes. The lower or southern portion of the county, like that on the north, is much improved by liming. Belts of limestone are found near New Providence and at Quarryville. Gneiss has much the composition of Granite, but with the Mica more or less distinctly in layers. As the Mica is in scales, a gneiss rock breaks most easily in the direction of the Mica layers, thus affording slabs. As the earthy matter of all soils has been produced by the gradual decay, degradation, or crumbling down of previously existing rocks, it follows that whenever a soil rests immediately upon the rock from which it has been derived, it may be expected to partake more or less of the composition and character of the rock. I shall not attempt to speculate on the cause and description of the diversified rocks, the convulsions to which they were subjected, in a remote period of the world's history, the faults, upheavings, &c., these subjects being accessible in the various books and treatises on geology.

MINERALS OF LANCASTER COUNTY.1

Arranged according to the last edition of Dana's Mineralogy. To give the general reader an idea of the nature and composition of each mineral, its constituent elements are stated in a parenthesis, without regard to chemical combination. When the occurrence of a mineral is rare, or the locality new or doubtful, the authorities are given in initial letters: D. standing for Dana; K. for Kevinski; R. for Miles Rock; Ræ. for Ræpper and W. for Captain Williams.

I. NATIVE ELEMENTS.

1. GRAPHITE, or plumbago, (carbon,) K.

II. SULPHIDES.

GALENITE, or galena, (lead, sulphur.)

1. Contributed by Mr. J. B. Kevinski.