Reports and Proceedings—Geological Society of London, 285 
Limestone; but in the third area they are mostly in the Yoredale 
Shales, and lava plays only a subordinate part. In the Miller’s Dale 
area the upper lava is the thicker, and extends over a greater district 
than the lower, while in the Matlock area the converse is true. In 
the former area the lavas are separated by about 150 feet of limestone, 
in the latter by about 80 to 100 feet. The upper lava of Miller’s 
Dale is on a lower horizon than the lower lava of Matlock, and the 
limestone above it contains at least two bands of interbedded tuff. 
The lavas are vesicular and amygdaloidal in structure, and often very 
much decomposed. ‘They contain olivine, augite, and felspars, 
magnetite and iron-oxide; the felspars are often present in two. 
generations. The sills are, for the most part, ophitic olivine dolerites, 
and pass from a very coarse-grained dolerite through the intervening 
stages into a fine-grained dolerite or basalt ; they are similar in 
structure to certain Tertiary dolerites. The following vents are 
described :—In the north-western area, those at Speedwell, Monks 
Dale, and Calton Hill; in the south-east, at Cracknowl, the Grange 
Mill vents, Ember Lane, Moor Lane, and the Hopton vent; in the 
south-west, Kniveton Wood Cottage, Woodeaves, and Wibben Hill. 
The majority of the vents are composed of volcanic agglomerate ; but. 
the Calton vent, near Miller’s Dale, is a typical basalt with a small 
portion of agelomerate, and the Hopton vent is a breccia of basalt 
fragments. The Toadstones have all been mapped on the 6-inch 
scale, and petrological accounts of the different rocks are furnished. 
2. ‘Data bearimg on the Age of Niagara Falls.’’ By Professor: 
Joseph William Winthrop Spencer, A.M., Ph.D., F.G.S. 
The author has been engaged in investigations for a monograph 
on Niagara Falls, to be published by the Geological Survey of Canada. 
Soundings at all the points of great changes in the Gorge have been 
successfully undertaken, borings were put down for the exploration 
of buried valleys, and instrumental surv eys made of the original river 
banks and the physics of the stream. The mean recession of the 
crest-line of the Falls is found to be 4:2 feet a year under existing 
conditions, and this rate has approximately obtained for 227 years. 
But this rate will not give the age of the Falls, on account of former 
great variations in the volume of the river and in the height of the 
Falls themselves. The chief change in volume of water depends on 
the fact that originally Lake Erie alone was discharged over the Falls, 
when the supply of water was only 15 per cent. of the present 
discharge. Luke Ontario, too, stood at a higher level, and thus the 
cutting back from Queenstown to Foster’s Flats was effected with 
a small water discharge and, at first, a low head. After an uphft 
which raised the crest of the fall considerably above Lake Ontario, 
a slight depression followed which ‘drowned’ part of the lower gorge. 
This cutting is calculated to have taken 35,500 years for a distance of 
14,400 feet. Above Foster’s Flats the sudden widening indicates the 
inflow of the other lakes into Erie, greater water discharge, and 
greatly increased rapidity of recession. The changes in height of the. 
Falls and resistance of the rocks are examined in detail, and the small 
influence of pre-Glacial filled channels estimated. ‘The Whirlpool is 
on the site where the recession broke down the partition separating 
