﻿Geology and Natural History. 409 



thus an excellent volume for the State, and a valuable one for the 

 geologist. Its many maps and other illustrations make it easily- 

 intelligible and supply much information to the eye. Mr. Ash- 

 burner's chapter on the anthracite and other regions show briefly 

 what has been accomplished, and reviews in an instructive way 

 the composition and fuel value of the coal. A very interesting 

 chapter by Lesley and d'Invilliers, gives an account of a bed of 

 magnetite in the Triassic region of Cornwall, in Lebanon County, 

 300 feet below the surface and nearly 63 acres in estimated area, 

 which became magnetite from limonite by the heat of a trap 

 eruption, and whose original limonite was made through the 

 decay of a ferriferous limestone of the Triassic formation. 



The paper by Professor Lesley on rock-gas of western 

 Pennsylvania, its origin, pressure, quantity, composition and 

 fuel-value, supplements the important chapter by Mr. Carll, ex- 

 plaining many points about which there is much popular misun- 

 derstanding, and considering from a basis of facts the probable 

 future of gas-production in Pennsylvania, foretelling its rather 

 speedy exhaustion. 



Another paper by Professor Lesley, on the Delaware and Ches- 

 ter Kaolin beds, endeavors to explain the origin of these deposits 

 by reference to the known or the probable position of gneiss 

 ridges below the Paleozoic, and the subject leads to remarks on 

 the great amount of denudation in past time over the region, 

 through all periods to the present, and on the origin of kaolin 

 beds generally. As the kaolin beds are beneath or near 

 limestone belts the decay of the limestone, it is suggested, may 

 have helped forward by its liberated carbonic acid and in 

 other ways, the decay of the underlying gneisses. The necessity 

 of favorable conditions for the percolation of waters by oppor- 

 tunities for natural drainage is dwelt upon. The subject is an 

 interesting one and the discussion instructive. 



4. Catalogue of the Blastoidea in the Geological Department 

 of the British Museum, by Robert Etheridge, Jr., of the De- 

 partment of Geology, British Mus., and Herbert Carpenter of 

 Eton College. 322 pp. 4to, with 20 plates. London, 1886. — This 

 " catalogue" contains a very full account of the morphology of 

 the Blastoidea, a discussion of the systematic position of the 

 group, and a revision of the genera and species, with descriptions 

 and illustrations on the plates of their structure and of the species 

 mentioned. The authors are the highest British authority on the 

 subject and understand thoroughly the morphology of Echino- 

 derms. Their work is therefore one of high authority. Mr. Chas. 

 Wachsmuth has been over the same ground, as regards the subject 

 of structure, with like ability, and with the aid of the large diver- 

 sity of American forms. The authors say in their preface, " our 

 chief difficulty, the want of adequate material, was soon and simply 

 solved ; for Mr. Charles Wachsmuth, of Burlington, Iowa, whose 

 admirable work on the Palseocrinoids is known to every palaeon- 

 tologist, generously offered to place at our disposal a selected 



