712 THE AMERICAN NATURALIST.  [Vou. XXXII. 
Gustav Rose in 1852. Recent additions are exhibited for a 
time in a case provided for the purpose, before they are 
distributed in the general collection. 
The great collection of rocks is arranged in the Mineral 
Gallery, on account of the close relationship between minerals 
and rocks, and consists of the regulation hand specimens 
about 4 x 6 inches in size, mounted on tablets in desk cases, 
and large specimens illustrating rock masses, installed in wall 
cases at one end of the room. A new feature of the collection, 
and one of the highest importance in such a branch of science as 
petrology, is the series of specimens introductory to the study 
of rocks. This series illustrates the gradual development of 
the science, and the terms used in the description of rocks as 
far as is practicable by means of specimens. Printed descrip- 
tions are displayed beside the specimens, so that they supple- 
ment each other in a very clear manner. It is not likely that 
the general public takes very much interest yet in such collec- 
tions of rocks, but the demand for information on the subject 
of petrology is on the increase, as is shown by the testimony 
at the various museums mentioned in these notes, in which 
rock collections are on exhibition, and especially where the 
general collection is supplemented by an adequate introductory 
and explanatory series of specimens. 
The series of guidebooks published by the British Museum 
is a highly commendable feature of the institution. These 
little books, of which fourteen are now issued for the various 
departments of natural history, are valuable aids to any one 
examining the collections. A few of them are intended merely 
as indexes to the collections described, but most of them are 
veritable text-books in popular though accurate language intro- 
ductory to the department of science treated, making the most 
direct use from page to page of the specimens on exhibition in 
the cases. They are models of what explanatory guidebooks 
should be, and their prices are so low as to bring them within 
the means of all persons interested. 
The Jermyn Street Museum.—The “Museum of Practical 
Geology,” in Jermyn Street, contains the collection of the 
Geological Survey of the United Kingdom. In scope it 1s 
