Personal iinil Scientific Xeirs. 65 
In a recent paper in the Journal of Geology (vol. n, p. 142, Feb.- 
March, 1894), Mr. Andrew M. Hansen, of Norway, notes the approxi- 
mate concurrence of about thirty independent measurements and esti- 
mates of the length of the Postglacial period which have been made in 
North America and in Europe, all coming within the limits of 5,000 
and 12,000 years. He therefore says: -'With full regard to a legitimate 
calculation of probabilities, it may he predicated that the number of 
7,000 to 10,000 years is as nearly an exacl estimate of the duration of 
postglacial time as can ever be expected." Wahkkx Timiam. 
June 11th, 1S94. 
P. S. Since the foregoing was written, I learn, by a letter of June 
18th from Mr. Gilbert, that a narrower part (probably the original col) 
of the valley leading from lake Nipissing to the Ottawa is situated 
about ten miles east of the present water divide, where the Mattawa 
river, outflowing from Trout lake, is enclosed, near the mouth of that 
lake, by rocky hills. Mr. Gilbert also calls attention to the ureal depth 
of the Niagara river (having a maximum sounding of 185 feet) at the 
foot of the falls and for nearly two miles to the head of the "Whirlpool 
rapids. The deep excavation there below the river level, analogous to 
pot-hole erosion, he attributes to a probably larger volume of the river 
than that which previously formed the shallower and longer portion of 
the gorge, excepting only at the Whirlpool, where the postglacial gorge 
coincides with one'of preglacial age. Concerning the preglacial erosion 
along the course of the Niagara, Dr. Julius Pohlman has written in the 
Proc. A. A. A. S.. vol. xxxv, for 1886, pp. 221, 222. The greater thick- 
ness of the Niagara limestone at and near the falls than along the part 
of the gorge beyond the Whirlpool may probably account chiefly for the 
deeper excavation by the cataract now than during tie' earlj part of its 
recession. w. u. 
June gist, 1894. 
PERSONAL AND SCIENTIFIC NEWS. 
The Geological Society of America will hold its sixth 
summer meeting in Brooklyn, N. Y., Aug. 13-15; anil the 
American Association for the Advancement of Science will 
hold its forty- third meeting in the same city, Aug. 15-24. 
Several excursions for geologists are planned, affording oppor- 
tunities to study the Palisades of the Hudson, the Cretaceous 
strata of New Jersey and of State n and Long islands, and the 
terminal moraine of the ice-sheet. 
At a meeting of the Geological Society of France, May 
7th, 1894, M. Cayeux presented a preliminary note on theradi- 
olarians of the Pre-Cambrian of Bretagne. He finds thai they 
belong to the divisions Spumellaria and Nassellaria, the latter 
