1^.ASAL CONGLOMERATE IN PENx\SYLVANlA 519 



sylvania b 'tween Easton on the north and Kintiiersville on tlie south, liaving in 

 the main the same northeasterly and southwesterly trend. 



More detailed Descuiption of special Localities 



The northernmost of these ridges, Chestnut hill, lies north and west of Easton. 

 It consists largely of dense hornblende and augite gneisses, which dip at an angle 

 of from 40 to 60 degrees to the southeast. The ridge diminishes in altitude toward 

 the southwest and at a distance of 4^- miles from Easton disappears under the 

 Cambrian dolomites. Along the northern border of this ridge runs a typical break 

 thrust fault by which the pre-Cambrian gneisses are forced up over the Cambrian 

 dolomites, as a result of which the lowest member of the Cambrian (the conglom- 

 erate) is wanting. Movement of a somewhat different character has taken place 

 along the southern margin of the ridge, as a result of which the basal member is 

 here again wanting, except at two points — one on the Delaware river, where, faulted 

 in between a granite wall on the south and a gneissic wall on the north, is a slaty 

 mass of more or less ferruginous quartzite, showing under the microscope well 

 rounded grains of quartz having a cementing material of quartz (?) tinged with a 

 brownish or reddish dust of iron ore, which in the neighborhood of the walls has 

 been reduced by shearing to magnetite grains. The other occurrence lies at the 

 CKtreme southwestern end of Chestnut hill and constitutes a small, poorly defined 

 area of a similar kind of rock. These two occurrences may be interpreted as 

 showing the former extension of the lowest Cambrian over the northeasternmost 

 area of pre-Cambrian rocks, and as showing that its failure to appear continuously 

 is due to faulting and not to a lack of deposition. 



Two miles south of Easton lies the next most northerly ridge of pre-Cambrian 

 rocks, which continues with a single interruption at Shi inersville, in a southwesterly 

 direction across the southern portion of Northampton and Lehigh counties into 

 Berks. Along the northern margin of this area from the Delaware river to Beth- 

 lehem, with one exception (this on the Delaware river), no outcrops of the basal 

 conglomerate or quartzite occur; but from Bethlehem toward the southwest it in- 

 creases in importance, and it is from this region that I desire more particularly to 

 select occurrences for special consideration. At no one place could all of the dif- 

 ferent phases of the basal series be found in undisturbed stratigraphic sequence; 

 neither could their total nor their individual thickness in any case be accurately 

 measured; yet, in considering the dip of the beds and the relative distance of a 

 given outcrop from the underlying pre-Cambrian gneisses, some conclusion could 

 be arrived at, both as to the relative position of the beds and to their total thickness. 



The following is a description of some of the more striking characteristics or 

 phases of the basal series as exhibited at a few of the more typical localities, and, 

 so far as could be determined, they are described in the order of their sequence, 

 beginning with the lowest. 



One mile northwest of Vera Cruz, in Lehigh county, is to be found a coarse 

 pebbly conglomerate, consisting of rounded, sometimes also more or less angular, 

 pebbles and fragments of quartz and feldspar, the pebbles occasionally having a 

 diameter of 2 or 3 inches, the same imbedded in matrix of finer materials consist- 

 ing also of quartz and feldspar. This seems to be quite uniformly the character 

 of the lowest member of the series, and in a number of instances it was found to 



LXXII— Bull. Geol. Boc. Am., Vol. 14, 1902 



