1890.] NATURAL SCIENCES OF PHILADELPHIA. 191 



street ])ridge.s over the Schuylkill also in a boring made l)elo\v the 

 bottom of the Schuylkill in searching for a suitable foundation for the 

 central j)ier of the pivot bridge at Penrose Ferry. These borings 

 Avere furnished by S. L. Smedley, City Surveyor. IMarine and fresh 

 water diatoms were also met with in abundance near Reed street 

 wharf on the Dehiware river in clay from an excavation twenty feet 

 or more in depth made for the construction of a water tank for the 

 use of Spreckels' Sugar Refinery. 



Dr. F. W. Lewis in the Proceedings for 1861 evidently refers to 

 this same deposit when on page 62 he says : " The old estuary bed 

 of the Delaware (blue clay) was very rich in these forms" (i. e. brack- 

 ish and marine) " and by digging down a short distance at any part 

 of the meadowland bordering the river the blue clay which contains 

 them may be exposed." 



In connection with these remarks, and as completing the record of 

 discoveries relating to diatoms in Philadelphia clays, it may be well 

 to refer to an exclusive fresh water deposit brought to the notice of 

 the Academy by Prof G. A. Koenig, in November, 1885, and by 

 Aubrey H. Smith in May, 1886. This was found in the bottom of 

 the cut of the Baltimore and Ohio R. R. south of Gray's Ferry road. 

 The same bed has since been seen by the speaker in the bottom of 

 an excavation made for Reed street sewer near where it passes under 

 the Baltimore and Ohio R. R. and about three blocks from the 

 former locality. 



This fresh water bed occupies a higher level than the marine depos- 

 its bordering the rivers. It underlies the clays used for brick mak- 

 ing in the vicinity, and is separated therefrom by a few feet of gravel 

 and must itself lie very close to or upon the micaceous rocks under- 

 lying and surrounding the city, and which outcrop between tlie points 

 where the deposit has been observed and the Schuylkill River. 

 From information obtained from workmen at the locality the bed is 

 believed to be about ten feet thick. Its exact relation to the marine 

 and mixed deposits previously described in this communication has 

 not yet been determined. 



June 24. 

 Mr. Charles Morris in the chair. 

 Seventy-six persons present. 



Mexican Explorations.— Frof. Angelo Heilprin made a prelimi- 

 nary report on the work accomplished by the exploring party which 

 went to Mexico in February last. It was announced that detailed 

 reports of the expedition were being prepared and would be pre- 

 sented for publication later in the year. 



Mr. J. Dundas Lippincott was elected a member. 



The following was ordered to be printed : — 



