308 surgeons' reports — Pennsylvania — seventh district. 



geological features. The northeru part is gcuerally rugged and hilly. The soil varies from a stiff 

 to a sandy loam, and is for the most part very fertile and highly cultivated. Somewhat north of 

 the center of the county is the North Valley Hill, which has a northeast and southwest direction, 

 at the southern base of which lies the Great Valley, which varies from one to three miles in width. 

 South of this is another range, called the Slate Ridge, which observes a course parallel with the 

 before-mentioned hill occurring north of the valley. These hills form two parallel ridges, which 

 shnt iu the Great Valley ; the soil of the latter is a light sandy loam, and highly fertile. The 

 surface of the southern portion of the county, with a few exceptions, is rolling ; and, except where 

 tiie mica and talc slates prevail, the soil is highly fertile, and is, for the most part, a sandy loam. 



All that part of Chester County lying south of the Great Valley, and which may be said to 

 embracemorethauone-half of its are;i, is made upof rocks which belong to theprimary stratified group. 

 These consist chieily of gneiss, with a small belt of mica and talc slates ; the latter lying in con- 

 tact with the prim.ary limestone of the Great Valley, and bounding the gneiss on the north and 

 west. Small beds of limestone, frequently possessing a crystalline character, but generally more 

 or less altered iu structure, are numerously scattered throughout this formation, with here and 

 there a spur or ridge of serpentine. The first belt of gneiss enters Chester County on the east, 

 from the adjoining county of Delaware, and from New Castle County, Delaware, on the southeast 

 and south, and gradually expanding in a northeast and southwest direction. It embraces the 

 whole of the townships of Easttowu, Westtown, Thombury, and Eirmiugham, and more tlian the 

 southern half of the townships of Willistowu, East and West Gosheiv, and East and West Brad- 

 ford, where it reaches the Braiidywine Creek. After crossing the creek, the belt rapidly widens, 

 and occupies all the townships of Pennsbury, Pocopson, Newlin, East and West Marlborough, 

 Kennett, New Garden, Penn, and London Grove. 



Bounding the northern and western extremities of the gneiss, and itnmediately in contact with 

 the southern margin of the primitive limestone of the Great Valley, is the talc and mica slate 

 range. The mica and talc slates enter Chester County at its northeast extremity from the adjoin- 

 ing county of Montgomery by a narrow zone about one mile iu width, and, i)assiiig acioss the 

 county in a northeast and southwest direction, graduallj' widening as it proceeds, it occupies the 

 southern margins of the townships of East and West Whiteland, East Cain, the northern parts 

 of Easttowu, Willistowu, East and West Goshen, East and West Bradford, Uighland, and East 

 and West Fallowtield, where it rapidly expands and passes west into the southern jiart of Lancas- 

 ter County. In the township of West Faliowfield, the belts of talc and mica slate are suddenly 

 deflected to the south ; embracing nearly the western half of the townships of Upper and Lower 

 Oxford and East and West Nottingham, it passes out of the southwestern border of the county 

 into Cecil County, Maryland. The townships of London, Britain, Franklin, New London, and the 

 greater part of East and West Nottingham, Upper and Lower Oxford, and Londonderry, are 

 occupied by gneiss and mica slates, interspersed with occasional belts of hornblende and stratified 

 syenitic rock. In numerous i)laces in the northeast i)art of the county, there exist large beds of 

 hemutitic iron-ore. Crystallize i plumbago occurs in several of the iron-mines, and is also dissemi- 

 nated through the quartz of the surfa('e. 



Somewhat to the north of the center of the county, and extending across by a narrow belt, 

 varying from one to three miles in width, is the primitive limestone which forms the Great Valley. 

 The iron and copper mines yield a large luunber of very beautirnl and interesting varieties of 

 minerals, which it would be out of place here to enumerate. 



* * * The. diseases most common in this district are the vaiious alfections of tlie 

 respiratory organs in winter and spring, and disorders of the digestive organs iu summer and 

 autumn. Along the Delaware Itiver, and confined mostly to the marsh lands and their vicinity, 

 intermittent and leiuittent fevers prevail. Dysentery is common in all parts of the district. 

 Typhoidal fevers occur every year eudemically. 



After careful examination and comiiarison of each, I am impelled to the belief that the diseases 

 of this district are not in any manner influenced by geological formations, except that intermittent 

 and remittent fevers have lieen confined to marsh lands on the Delaware River generally. 



Prevailing diseases of ISOi. — Pneumonia and other catarrhal affections were frequent during 

 the severe cold weather of winter. Sporadic cases of dii)htheria were quite frequent. During 



