102 The American Geologist. February. i89:t 
source is in a sandstone of the Cherokee shales, or near the bottom 
of the coal measures. It proves to be a terrace of well marked char- 
acter. For seven miles the top of the gas rock has an elevation of 131 
feet above tide, rising at no point more than 45 feet above this. At 
this summit, the largest well of the field is located, yielding 10,000,000 
cubic feet per day. The gas is being largely used by the lead and 
zinc smelters of the Joplin district. 
" The Conshohocken Plastic Clays," by T. C Hopkins, 
State College, Pa. The plastic clays near Conshohocken, Pa., form an 
isolated deposit. The resemblances to the New Jersey and Gay Head 
clays in colors, texture and structural features suggest clays of the 
same age. The location and character of the deposits were briefly 
described. 
Gotd Mining: i" the Klondike District; by J. Y>. Tyr- 
rell. Canadian geological survey. The geology of the Klondike 
region was described and illustrated with lantern views made from 
photographs taken by the author last summer. He stated that the 
stream gravels were of the usual type of gravels, but that the bench 
gravels were lateral moraines left by glaciers and that the gold con- 
tent had not been transported from a distance. 
Ripfite-Marks and cross bedding; by G. K. Gilbert, U. S. 
geological survey. The general theory of ripple-marks as developed 
by Darwin and others was stated and illustrated by means of dia- 
grams. The relation of the dimensions of ripple marks to the waves 
causing them was stated to be, in general, that the distance from 
crest to crest of the ripple marks is one-half the hight of the waves 
making them. The author referred certain large undulations in the 
Medina sandstones near Lockport, N. Y., to ripple marks. A lantern 
slide of one of these giant ripple marks 23 feet across and 29 inches deep 
was shown. Others must have been 30 feet across, indicating waves 
60 feet high in the Medina seas. When the waves are interfered with 
by currents confused ripple marks result. 
" The Glacial Lake of the Nashua Valley;' by W. O. 
Crosby, Massachusetts Institute of Technology. The Nashua is the 
largest stream east of the Hudson-Champlain valley, flowing through- 
out the main part of its course in a northerly direction, and the up- 
per part, especially, of its valley is deep and well defined, presenting, 
thus, ideal conditions for the development of the phenomena of glacial 
lakes. The penr-up waters were effluent first southward at elevations 
successively of 760 and 440 feet, being then tributary to the Blackstone 
river and Narragansett bay; and later southeastward at an elevation 
of 370 feet through the pass now occupied by the Central Massa- 
chusetts railroad. This was the principal and most persistent stage 
of the lake; and the effluent waters were probably, through the similar 
l)locking of the Assabet and Sudbury valleys by the ice-sheet, forced 
across the country into the valley of the Charles river and Massa- 
chusetts bay. During this stage of the lake extensive delta plains 
