906 
Yorkshire flora, it is a characteristic element 
of the lower Oolite. i 
Sagenopteris Nilsoniana, while found in the 
Oroville flora, is most eharacteristic of the> 
Rhetic, and it does not occur in the Yorkshire 
Oolite, where its nearest representative is S. 
Phillipsi of Brongniart. Its reference to the 
Oroville horizon is regarded by Ward with 
some doubt, hence it can not be held to have 
much weight as a factor in determining age. 
The author concludes his valuable contribu- 
tion by a tabular view of the distribution of 
188 separate forms of Lower Mesozoic plants, 
showing their relation to the various North 
American areas both of the Triassic and Jur- 
assic formations. He thereby gives emphasis to 
the fact that remarkably few species (three) are 
common to both, formations, while even the 
majority of these are open to question. A com- 
parison of the flora of the Yorkshire Oolite 
with the Jurassic of North America shows that 
with respect to the Filices and the Conifer 
there is a close correspondence in relative num- 
ber of representatives, but that in the North 
American Jurassic there is a pronounced pre- 
ponderance of the Cycadacez. In the latter 
flora also, both Bryophyta and Equisetales ap- 
pear to be wanting. 
Inferior Oolite North American 
of Yorkshire. Jurassic. 
Bryophyta, 1 0 
Equisetales, 2 0) 
Filices, 20 15 
Cycadales 23 30 
Coniferze, 9 a 
D. P. PENHALLOW. 
MONTREAL, May, 1901. 
Steam-boiler Economy. A Treatise on the Theory 
and Practice of Fuel Economy in the Opera- 
tion of Steam-Boilers. By WILLIAM KENT, 
A.M., M.E. New York and London, John 
Wiley & Sons and Chapman & Hall. 1901. 
8vyo. Pp. xiv-+ 458. Price, $4.00. 
This is a work, by an authority in its field, 
devoted to the study, theoretical, practical and 
experimental, of steam-boiler economics. Its 
author has had a long and varied experience of 
the most valuable kind in this department of 
mechanical engineering and in related fields of 
work, study and research. To this peculiarly 
SCIENCE... 
(N.S. Vou. XIII. - No. 336. 
happy practical and theoretical acquaintance 
swith this subject he has added a singularly ex- 
ceptional talent for the work and an unusually 
thorough technical preparation for its prosecu- 
tion. Large experience, as an author and as an 
editor, and in the preparation of professiona! re- 
ports as expert in this and related matters, has 
given him the ability to digest, to formulate and 
to logically plan and execute a piece of techni- 
cal work of high grade. The outcome of his 
endeavor is an exceptionally condensed, com- 
plete and exact treatise. The author has also 
confined himself very closely to his restricted 
title, and the reader will find there precisely 
what he seeks. , 
The book is not only well constructed, but it 
adds to existing knowledge, as presented in the 
text-books and special treatises as commonly 
written, some very valuable novelties which 
have peculiar interest to the professional man 
and the student. For example, maps are given 
of the coal-fields of the country and the distri- 
bution of the fossil fuels is exhibited clearly ; 
while accompanying tables of composition, very 
full and officially endorsed, show what varia- 
tions of quality occur as we pass from the 
graphitic anthracites of Rhode Island and 
Massachusetts, across the Pennsylvania beds 
over the remarkable deposits of West Virginia 
and into the Alabamian district, or across Ohio, 
Indiana and Illinois, Tennesse and Kentucky 
deposits into the regions of the friable fuels of 
the Rocky Mountains and to the Pacific Coast, 
with its extensive distribution of lean coals and 
lignites. 
Mr. Kent has constructed some remarkably 
valuable as well as novel graphic illustrations 
of the laws connecting composition with effi- 
ciency with varying intensities of draught and 
variations of air-supply, and has done much to 
reconcile the widely differing conclusions of in- 
vestigators in this department of scientific re- 
search, who are now coming to be numerous 
and industrious, commensurately with a grow- 
ing recognition of-the importance of the sub- 
ject. He has given us a larger addition to our 
systematized knowledge, and has added to our 
obligations by introducing well-established and 
new and useful formulas and diagrams, express- 
ing the relations of conditions bearing upon and 
