September 23, 1897] 



NATURE 



497 



segregative and intrusive types are mixed together. 

 This prehminary study is followed up by Prof. Williams' 

 student, Mr. C. R. Keyes, in a detailed description of the 

 binary or true granites, granitites, and hornblende- 

 granites of Maryland. This writer insists that both 

 primary and secondary muscovite occur in the granites, 

 and that the intimate intergrowths of allanite and orthite 

 are original and not secondary products. The bed-like 

 or "sheeted" and spheroidal joints are described and 

 illustrated, and it is made quite clear that the rocks are 

 of igneous origin, locally affected by shearing, so as to 

 pass into gneissose and schistose rocks. 



Mr. Lawson's paper on the Geology of the San 

 Francisco Peninsula is deserving of attention at the 

 present time, when cherts and other radiolarian rocks 

 are being so much studied in Britain. Mesozoic rocks, 

 the Franciscan series, rest unconformably on the Montara 

 granite, which, in its turn, is intrusive into crystalline 

 limestone. The Franciscan series consists of sandstones, 

 in the interstital matter of which important reconstruction 

 has occurred, foraminiferal limestones, radiolarian cherts, 

 and volcanic rocks, partly intrusive and partly inter- 

 bedded, and often exhibiting characters similar to the 

 " pillow lavas " which occur in Britain in association with 

 cherts. The latter rocks, which range from holocrystal- 

 line aggregates of quartz granules to masses of isotropic 

 silica, are well banded and associated with what the 

 author calls shales, although " the highest powers of the 

 microscope fail to reveal any clastic material " in them, 

 and he is driven to admit that it is only the interbedding 

 of the cherts with common sandstone which checks the 

 supposition that they are deep-sea deposits. He inclines 

 to the view that the silica has been mainly derived 

 from submarine, siliceous springs. The rocks of this 

 series, where associated with intrusive peridotites, pass 

 into micaceous, chloritic, and amphibolic schists. An 

 excerpt from some notes of Dr. Hinde shows that he has 

 compared the radiolaria with forms from Jurassic and 

 Cretaceous rocks in Switzerland and Hungary. A short 

 account of the serpentines, the later bedded rocks, the 

 diastrophic record, and geomorphy concludes the memoir. 



The preliminary report on the Marquette iron-bearing 

 district of Michigan, while illustrating the use of local 

 names in accurately defining particular terranes, certainly 

 makes one wish that such of the terms as are likely to 

 become of larger importance were less cacophonous. 

 The Wewe slate, the Ajibik quartzite, the Bijiki and 

 Kitchi schist, of this paper, the Rappahannock and 

 Aquia Creek series of another paper, suggest a large 

 field of work for the International Congress in the 

 special effort at simplification of nomenclature which 

 it is making at St. Petersburg. The basement series 

 of granites and gneisses is separated by an uncon- 

 formity from the lower Marquette, and that by another 

 from the upper Marquette series, all these systems 

 being folded together in a complicated fashion which 

 has not yet been unravelled. The two Marquette 

 series are correlated with the upper and lower Huronian 

 systems. The bulk of the iron ores, which consist of 

 specular iron and magnetite, occur in the Negaunee 

 formation of the lower series, and below the Goodrich 

 quartzite ; but they frequently extend above and much 

 more often below, into the numerous beds overlapped 

 l)y quartzite. They have been formed by the concentra- 

 tion of iron ore in a cherty carbonate of iron, governed 

 by the folding of the rocks and the position of intrusive 

 diorite dykes. 



Mr. Lester F. Ward contributes a memoir on the 

 Potomac formation to the fifteenth report, and a cor- 

 relation paper on its analogies to the lower Cretaceous 

 rocks of Europe to the sixteenth report. The general 

 order of succession is studied, and the floras dealt with 

 in detail by the help of tables, plates, and descriptions 

 of new species. The tables lead the author to conclude 



that the floras compare with the Kome and Atane beds 

 of Greenland, and comprise the interval between these 

 two. The correlation paper is accompanied by beautiful 

 colour-printed geological maps of of South-east England 

 and the Isle of Wight, the author considering that the 

 Potomac formation is about equivalent to the Wealden 



j series. Further comparison is instituted with Cretaceous 

 floras in Italy, and Cretaceous and Jurassic floras in 



( Portugal. 



Under Mr. Walcott's direction the publications of the 

 Survey at once become more specialised. One large 



t volume is devoted to purely scientific work, two parts of 



I another to mineral statistics and related papers, and a 

 third to memoirs mainly of an economical character. This 



I has led to a development in the character of the papers. 



; Those of an economic character tend to become more 

 useful to the agriculturist, the miner, and the road- 



j master, while the rest are written in such a way as to 

 be not only of value to the scientific man and popular 

 for the public, but to have an educational character, 

 being evidently written with a view of placing new ideas 



I and methods of work before both official geologists and 



; amateurs. As an example of the latter, we may cite the 

 pre-Cambrian paper, by Mr. Van Hise ; of the former, 



I those on road-stones, by Prof. Shaler, and the mining 

 papers in the economic volume. 



In dealing with road-metal, Prof. Shaler shows 

 that the tests of crushing strength usually made in 

 Britain and elsewhere, while of great value for building 

 stones, do not express all that is required with regard 

 to material for roads. Bits of stone are placed in a 

 drum, which is overturned at the rate of 33J revolutions 

 per minute, and the powder is collected and weighed. 

 The binding power of the dust is further tested by making 

 briquettes, which are broken and then crushed, moulded, 

 and broken again as often as necessary. This gives a 

 fair idea of the staying power of any particular stone for 

 different kinds of traffic, and enables the geologist, after 

 further petrographical examination, to express a pretty 

 decisive opinion on the merits of different metalling 

 stones. Study of sections of roads shows that great 

 attention ought to be paid to the gradual building up of 

 metal, and that in many cases it would be advisable to 

 mix softer binding stone with tougher metals on which 

 the steam-roller has little crushing effect. An account 

 of road metals and paving clays in Massachusetts is 

 given in the sixteenth report, and of the United States 

 generally in the fifteenth. 



A very valuable report on the Cripple Creek mining 

 district is given by Mr. Whitman Cross and Mr. Penrose, 

 the former dealing with the general geology, the latter 

 with the mining geology. Through a platform of granites 

 and schists a volcano opened in Tertiary times, and 

 ejected at first andesites and then phonolites, basalts, and 

 rhyolites in an order which cannot be precisely ascer- 

 tained, owing to the removal of lava streams by denuda- 

 tion leaving only dyke rocks behind. A sentence in the 

 introduction shows that scientific terms taken into 

 ordinar>' use suffer an even worse fate than ordinary terms 

 which have been adopted for scientific use. In Eng- 

 land the term granite, and in Ireland diorite, are used as 

 almost synonymous with road-metal, the former being 

 applied to everything from basalts to greywackes, and 

 from porphyroids to hard sandstones. Similarly the 

 word porphyry, originally meaning a purple rock, was 

 first applied to a purple rock with " porphyritic " crystals 

 in it, then to a ground mass like that embedding the 

 crystals, whether the latter were present or not. Now, 

 Mr. \'an Hise quotes a miner's definition that "porphyry 

 — well, porphyry generally runs three or four dollars " of 

 gold to the ton. 



The phonolites, which are intimately connected with 

 gold deposits, are fully described ; they contain abund- 

 ance of felspar, nepheline, sodalite, a^girine, and a blue 



NO. 1456, VOL. 56] 



