300 The American Geologist N mber.iaos 
cite and dolomite which furnish the mam source oi the 
serpentine. In Bucks county there are two small serpen- 
tine anas on the west hank oi Neshaminy creek, which are 
products of the alteration oi basic intrusive*. The north- 
em - ss ciated with gabbro and the southern area is in- 
trusive in the \\ issahickon inica-gn< ss 
rhe serpentines of the Philadelphia belt oi crystalline 
recks occur in a series oi dykes which extend through Mont- 
gomery county into Delaware and Chester counties; they 
will be described in detail later. 
The so-called state line serpentines are a continuation 
of one of these dykes, Thej extend for sixteen miles along 
the boundary between Pennsylvania and Maryland, begin- 
ning in Chester county, at Little Elk creek, and extending 
into Lancaster county and southwest into Cecil county. 
Maryland/ These like the other serpentines red 
eruptives.t Tl. e\ are associated with pyroxenytes and 
peridotytes and they represent the alteration product of 
these rocks. From Cecil count) westward through Har- 
ford 1 " 1 and Baltimore counties, southwest along the base 
oi Parrs ridge, across Howard and Montgomery counties to 
the Potomac They are secondary products of both pyrox- 
enytes and peridotytes. 
Delaware, — From the northeast corner of Delaware. 
extending southwest into Maryland is a helt of gabbro and 
associated rock types.* At Chestnut Hill and Iron Hill the 
peridotyte is serpentinised. In Delaware there is one other 
serpentine area. It lies in northern Xew Castle county east 
of Red Clay creek. It is intrusive in the mica-gneiss and 
with it as is frequently the case, are associated pegmatytes 
which may represent the most acid phase of the magma of 
which the mother rock of serpentine is the most basic 
Virginia. — In Virginia W. B. Rogers has described ser- 
pentine from the soapstone rocks of Nelson* and Amherst 
counties. 
* Bull. 13, Geo. Soc. Amer. 
t F D. Chester. ]'. una. Geol. Surv.. Ann. Rept., 1887, pp. 93-105. 
i Maryland Geol. Surv., Rept. of Cecil Do., F. B*sooa, 
* Am. Geol.. July. 189ft. The Non-Feldspathic Intrusive rocks of 
Maryland, by GK H Wulukb 
t These serpentines have been described by Dr. A. j«-ha\\se\ in an 
elaborate paper which has not vet been nublished. 
i Bull. 59. D. S. G. S.. 1896, by Frederick D. Chister 
