520 PROCEKDIXGS OF THK \VASHIN(iTOX MEETING 



pass by almost iinpercei)til)le gralati(jus over into the underlying granitoid gneiss 

 in sach a manner as to suggest the decidedly rapid submergence of a deeply 

 weathered Cambrian land mass, with a correspondingly rapid advance of the sea 

 over the same, affording insufficient time for the thorough sorting of the loose mate- 

 rials already at hand or the bringing in of any considerable amount of sediment 

 from a distance. The entire basal series, here representing as it does distinctly 

 littoral or at least shallow water deposits, has a total thickness of only a few hun- 

 dred feet at the most, and the conditions under which it was deposited must have 

 rapidly changed to those necessary for the deposition of the offshore and distinctly 

 deep water sediments represented by 2,000 or 3,000 feet of dolomites and dolomitic 

 limestones which immediately succeed it. 



At Macungie, 2 miles farther west, we find a rather fine grained bluish or grayish 

 cpiartzite, which weathers superficially to a brownish color, lying apparently above 

 the horizon of the conglomerate just described. The beds approach a horizontal 

 position, dipping at an angle of about 15 degrees to the north. It gives evidence 

 microscopically of a considerable amount of squeezing and stretching, as shown in 

 a well defined cleavage and occasionally in a sort of stringy or fibrous appearance. 

 Under the microscope the grains of quartz are seen to be much broken and crushed, 

 or it may be drawn out so as to have one much elongated diameter. The wavy or 

 undulating extinction of the larger plates is very pronounced, and a cataclastic 

 structure is sometimes beautifully developed. 



With the quartz occurs quite uniformly at least a small amount of feldspar. This 

 constituent frequently becomes of primary importance, in which cases the rock 

 assumes the character of an arkose. This phase of the basal conglomerate is often 

 the prominent one. The feldspar is usually kaolinized, and in weathered specimens 

 appears as white, floury points and blotches scattered through the rock. It is 

 sometimes fresh enough, however, to be determined under the microscope as ortho- 

 clase or raicrocline. As accessory minerals might be mentioned an occasional flake 

 of biotite or muscovite, with here and there a fragment of rutile or a grain of zircon 

 or of titanite. The cementing material, which is very meager, is silicious. 



Two miles farther west, at Alburtis, the same beds furnish even better exposures 

 than at Macungie. Here, as the result of a slightly overturned fold, beds dip at 

 an angle of from 70 degrees to 85 degrees to the south and toward the gneiss. 

 They can be traced to the west almost continuously by good outcrops across the 

 Berks county line to a point 1 mile south of Shamrock, Here, iiiterstratified with 

 a rather coarsely granular bluish or grayish quartzite, are a few feet of impure, 

 very fine grained, argillaceous quartzite, filled with the casts of worm borings 

 (scolithus). This is the only fossil thus far discovered at any of the above named 

 localities in the basal series. It is hoped, however, that a continued search will 

 discover some distinctively Lower Cambrian species. 



This is the most favorable locality within the area described for obtaining an 

 estimate of the thickness of the series. Here, measuring across the upturned edges 

 of the beds, we have an exposure about 50 feet thick ; and they are probably much 

 thicker, for in averaging the distance between this outcrop of quartzite and the 

 gneiss on the south side and the distance of the quartzite from the dolomite on 

 the north side we should have to assume a thickness of 300 feet or possibly several 

 hundred feet. 

 That member of the basal quartzite which in this region lies at the summit of 



