Geology of Hudson County, New Jersey. 29 



New York Bay, the drift is again concealed beneath simihir de- 

 posits, which are thus shown to be of a more recent date. 



Beginning with the oldest of these formations, and examining 

 each in the order of its age, we hope, by giving wliat facts we 

 have been able to gather concerning them, to find the position 

 occupied by each stratum in the geological column, and to indi- 

 cate at the same time the relation borne by the various forma- 

 tions to the prosperity and sanitary condition of Hudson 

 Couut}'. 



Arch^an Rocks. 



Gneiss mid Mica Schist. — Eocks of this class occur at the 

 very base of the geological column, and are among the oldest 

 strata known ; their general appearance is no doubt familiar to 

 most of my readers, from the abundant outcrops of these 

 rocks on Manhattan Island. Wherever the Archaean rock comes 

 to the surface in the neighbor!) ood of New York, it is usually 

 composed of highly crystalline gneiss, mica-schist, hornblende- 

 schist, marble, etc. ; all of these were at one time earthy or cal- 

 careous sediments, spread out in horizontal layers at the bottom 

 of the Archffian Ocean, and have since been upturned, folded 

 and crumpled into their present contorted forms. During these 

 changes in position, the strata have been altered and metamor- 

 phosed by the action of heat and heated solutions, so that they 

 now bear but little resemblance to the sand and mud of which 

 they were originally composed. The minerals now forming these 

 metamorphosed rocks are principally quartz, feldspar and mica, 

 and still retain in their arrangement some indication of the strati- 

 fied nature of the original deposits. Some of our citizens still 

 remember a reef of this rock, formerly to be seen in Jersey City 

 at low tide, between Washington and Green Streets and north 

 of Harsimus Street ; this was a narrow crest, about one hundred 

 feet in length, with nearly vertical walls ; the mud near at hand 

 on either side being sixty feet deep. From specimens recently 

 obtained, we learn that the rock forming this reef varied con- 

 siderably in appearance, some of it being a typical mica-schist, 

 with well-defined layers of mica, etc., while other portions were 

 of gneiss appearing so compact and fine-grained that they re- 



