272 



NATURE 



IJan. 25, 1877 



neous interpretations, are quoted with simple faith by Dr. 

 Packard ; so, too, are the same author's observations on 

 Gasteropod development. 



Page 105. — A serious error is here revived as to the 

 identity of the velum of the Gasteropod larva, and the 

 wings of such Pteropods as Styliola. The older observa- 

 tions of Gegenbaur, and the later ones of Fol, have shown 

 that the velum co-exists with, and is quite distinct from, 

 the expanded wing-like foot-lobes of the Pteropods. 



Page 117. — The mode of development of Grenacher's 

 Cephalopod is not, as stated by Dr. Packard, " totally 

 different" from that of the common cuttle-fishes. It 

 differs only in the somewhat smaller size of the nutritive 

 yelk. The marginal cilia have no significance. 



Page 120. — " Peripatus has been proved by the re- 

 searches of Mr. Moseley to be a tracheate insect, for in 

 the young genuine tracheae exist, though they disappear 

 in the adult, or at least have not been discovered." We 

 should have expected to find Dr. Packard less inaccurate 

 in what relates to the Arthropods. The above is altogether 

 misleading ; what Mr. Moseley found was that the adult 

 Peripatus is richly supplied with tracheae. He did not find 

 tracheae in the embryos, but he found still more import- 

 ant evidence of Arthropod character, namely, the pre- 

 sence of a pair of foot-jaws, the first post-oral pair of 

 appendages becoming modified in the course of develop- 

 ment, so as to function as mandibles. 



Page 207. — Amphioxus is said to possess " primitive 

 kidneys like the segmental organs of Worms." Of all the 

 varied attempts to fix upon renal organs in Amphioxus 

 there are none which quite warrant this statement. The 

 fact is that nothing corresponding to the segmental 

 organs of Worms has ever been described in Amphioxus, 

 excepting the " pigmented canals." Though sometimes 

 one epithelial area and sometimes another is declared for 

 the time to be " renal," functionally if not morphiologi- 

 cally, the truth is that no renal organs at all are known 

 to exist in Amphioxus. 



Notes like the preceding might be multiplied were it 

 worth while. Though such inaccuracy of statement does 

 somewhat lessen the value of Dr. Packard's book, it is 

 nevertheless one which is really welcome, and serves very 

 well the main purpose for which it was designed, viz., 

 that of conducting the commencing student over the 

 recent literature of that young giant, Comparative Em- 

 bryology. 



E. Ray Lankester 



OUR BOOK SHELF 



Descriptive Catalogue of a Collection of the Economic 

 Minerals of Canada^ and Notes on a Stratigraphical 

 Collection of Rocks. Exhibited at the Philadelphia 

 International Exhibition. (Montreal, 1876.) 



The geological survey of Canada, under the direction of 

 Mr. Selwyn, F.R.S., has placed in the Philadelphia 

 Exhibition a collection of minerals and rock specimens 

 of much interest, as they very fairly represent the geolo- 

 gical productions of the Dominion, as far as the opera- 

 tions of the survey have extended. The descriptivb 

 catalogue of these " exhibits " (we regret the use of this 

 new-fangled Americanism in a Canadian work) has been 

 ably drawn up by the Geological Corps of Canada under 

 the following heads : — I. Metals and their ores. 2. 



Materials used in the production of heat and light. 3. 

 Minerals applicable to certain chemical manufactures, 

 and their products. 4. Mineral manures. 5. Mineral 

 pigments and detergents. 6. Salt, brines, and mineral 

 waters. 7. Materials applicable to common and decora- 

 tive construction. 8. Refractory materials, pottery-clays, 

 and pottery. 9. Materials for grinding and polishing. 



10. Minerals applicable to the fine arts and to jewellery. 



11. Miscellaneous minerals. This catalogue is sufficiently 

 comprehensive, while the arrangement is well adapted for 

 easy reference. 



Along with the descriptions of the specimens under 

 each head we frequently find a condensed account of the 

 origin and progress of various industrial pursuits. Thus 

 under the head of Class 2, " Materials used in the pro- 

 duction of heat and light," we have short notices of the 

 more important collieries in the eastern provinces of 

 Canada, together with observations on the origin of the 

 petroleum springs of Ontario. The region in which the 

 petroleum beds occur is situated in the western part of 

 Ontario, around the town of Petrolia, occupying about 

 eleven square miles of level ground, covered to a depth of 

 about 100 feet with bluish clay. The oil is tapped by 

 borings, which penetrate a series of bluish dolomites, 

 shales, and marls to a depth of 380 feet under the clay, 

 when a productive stratum is struck, and the oil, accom- 

 panied by sulphurous saline water, flows into the bore- 

 hole, or well. The strata penetrated in boring the oil- 

 wells, belong apparently to the " Hamilton," " Chemung," 

 and " Portage " groups, representing according to Sir W. 

 Logan, the upper portion of our Devonian beds,^ but the 

 petroleum itself is believed to originate in the lime-stones 

 of the " Corniferous " lormation which lie underneath ; 

 the strata occur in the form of a flattened dome. An- 

 other source of petroleum is the " Trenton " group, much 

 lower down in the geological series, and referable to the 

 Lower Silurian period. The geological position of the 

 petroleum beds, as well as cases of actual observation, all 

 go to show that the source of the mineral oil is animal, 

 not vegetable. The limestones of the Corniferous, Gasp^, 

 and Trenton groups are more or less coralline, and from 

 the observations which Sir W. Logan records, it would 

 appear that the oil is derived from the decomposition of 

 the animal matter which originally filled the cells of the 

 coral-rock. In such a position the oil has been observed, 

 where these palaeozoic limestones crop out at the surface, 

 and where the limestone is overlaid by sandstone, as in 

 the United States, or by shales or other materials, as in 

 Canada, The animal oil has saturated these latter to such 

 a degree that they have become underground reservoirs 

 which can be made available by artificial means. 



The notes by Mr. Selwyn on the collection of rock- 

 specimens suggest several points on which we should like 

 to dwell, did space permit. We shall only, however, refer 

 to the remarkable case of metamorphic action to which 

 he calls attention ; namely, that to the south-east of the 

 Valley of the St. Lawrence the formations are highly 

 metamorphosed, their representatives to the north of that 

 river being in their unaltered condition. This change 

 takes place along a great line of dislocation ranging from 

 Lake Champlain to Quebec and Gaspe, as described by 

 Dr. Sterry Hunt. The change in the condition of these 

 beds, none of which are probably older than the Devonian 

 period, is so great, that the hand- specimens are undis- 

 tinguishable from others collected in Eastern Canada or 

 Ontario of undoubted Laurentian age. That metamor- 

 phic rocks may be of any geological period is a fact of 

 which students of geology should be reminded ; for we 

 have recently had evidence before us, that some of the 

 rising generation of geologists are still instructed in the 

 exceedingly erroneous view that there is a " metamorphic 

 system " of rocks forming the base of the general series. 



E. H. 

 "Geology of Canada," p. 20. 



