298 F. BASCOM — PIEDMONT DISTRICT OF PENNSYLVANIA 



Strati graphic relations. — The Chickies quartzite lies in an overturned 

 synclinorium on the northwest flank of the Baltimore gneiss anticli- 

 norium. It immediately overlies the Baltimore gneiss. There is no 

 appearance of unconformity between the two formations, save as uncon- 

 formity is indicated by the presence of the conglomerate member of the 

 quartzite formation. 



Thickness. — The thickness of the formation does not exceed and may 

 be less than 1,300 feet, although the isoclinal folding gives the appear- 

 ance of much greater thickness. Overturned folding with stratification 

 and cleavage dips to the southeast are the prevailing structures. The 

 average strike is north 50 to 70 degrees east and the dips 45 to 80 degrees 

 southeast. Faulting explains the disappearance of the quartzite on the 

 south limb of the anticline. 



Correlation and name. — The name of the formation is taken from the 

 locality of its finest exposure and greatest thickness on the Susquehanna 

 river north of Columbia. At this locality Scolithus linearis has been 

 found, which occurs also abundantly in the north Chester Valley hills, 

 and the quartzite of this locality underlies quartzite in which olenellus 

 fragments have been found by Mr Walcott,* thus fixing its age as Georgian 

 or lower Cambrian. The quartzite of the southeastern belt, tying farther 

 to the east than this typical exposure of Georgian quartzite on the Sus- 

 quehanna river, may have been deposited in an encroaching sea, and 

 thus represent a later horizon in the Cambrian than the Georgian. No 

 forms of life save Scolithus linearis have been found in it ; hence it can 

 not positively be stated to be of Georgian age. It can safely be stated 

 to be Cambrian, and is to be correlated with the Vermont quartzite of 

 New England, the'Poughquag quartzite of New York, and Setters quartzite 

 of Maryland. It is the " primal sandstone " of H. D. Rogers and " for- 

 mation number 1, Chickies sandstone," of the Second Geological Survey 

 of Pennsylvania. 



CAMBRO-ORDIV1CI AN ROCKS: CHESTER VALLEY LIMESTONE 



Distribution. — This is heavily bedded crystalline, white or bluemagne- 

 sian limestone. Its surface exposure is largely confined to Chester valley, 

 with a few scattered outcrops along the Huntington and Cream valley 

 fault lines, and to the southeast in Chester county and Delaware. The 

 presence of the limestone in Huntington valley along the course of 

 Meadow brook is indicated by the character of the well water. The 

 rock actually outcrops, however, only in the cellar of a wagon-house a 

 quarter of a mile northeast of Meadow Brook station. In Cream valley, 



* C. D. Walcott : The Cambrian rocks of Pennsylvania. Bulletin U. S. Geol. Survey, no. 134, 

 p. 17. 



