PUBLTCA TLONS. 869 
text and to the advertisements, all of which greatly increase its value 
as a reference book. 
The aim of the editor is shown in the following extract from the 
preface : 
The intention in preparing this work has been to collect and put in convenient 
form all the reliable statistics of the world; to collect more promptly and more accu- 
rately than had hitherto been done the mineral statistics of the United States ; and to 
photograph, as it were, the condition of the industry from year to year, bringing out 
into boldest relief that information which has the greatest practical value in the devel- 
opment of the industry and which is not easily accessible. . . . This work is above 
all things designed to be of actual value to the practitioner, to afford those engaged 
in mining, metallurgy, and industrial chemistry, a safe and authoritative guide which 
will keep them informed as to what is being done, and how it is done, in each depart- 
ment of the industry throughout the world. 
dts Creal: 
Honeycombed Limestones in Lake Huron. By RoBertT BELL. 
In the Bulletin of the Geological Society of America, Dr. Robert 
Bell describes the honeycombed limestone of Lake Huron. It is 
found chiefly about Manitoulin Island, Indian Peninsula, and the area 
between these and Georgian Bay. The formation progresses faster in 
water fifty or sixty feet deep, but takes place in shallow water. It is 
found on the under side of overhanging rocks as well as on other sur- 
faces. There are two principal forms of this erosion. In the first the 
cavities are elliptical, and neighboring ones tend to meet, giving a 
very spongy appearance. In the second the pits are finger like and 
crowded close together at the surface. They are usually shallow, but 
may be some inches in depth. The rocks in the vicinity of Manitoulin 
Island run from the Chazy to the Guelph. Dr. Bell finds the pits 
largest and most numerous in the dolomite of the Guelph formation. 
As to the immediate causes of the solution to which they are due, Dr. 
Bell cites an obscure concretionary structure in the rock, and an 
unusual amount of H,SO, and sulphates in the water. He attributes 
the source of the sulphur compounds to the Huronian rocks that lie 
on the north of the lake. These are in part volcanics and rich in sul- 
phides. He thinks solution is aided by hydrostatic pressure, free 
action of water and shifting currents. 
Critical Periods in the History of the Earth. By JoserpH L. LE 
CONTE. 
The thesis laid down by the author is that “‘There must have been. 
