March 19, 1896] 



NATURE 



465 



Volume xxiii. (1894) of the Monographs of the Survey 

 is devoted to the geology of the Green Mountains in 

 Massachusetts, by Messrs. Pumpelly, Wolflf, and Dale. 

 This district of Palaeozoic rocks is complicated by two 

 circumstances ; in the first place, the limestones of Grey- 

 lock Mountain appear to pass shoreward into the sandy 

 and shaly beds of Hoosac Mountain to the west, and in 

 the second place, metamorphism has proceeded much 

 further at the western end of the series. Resting on the 

 Stamford gneiss of Pre-Cambrian age comes the coarse 

 gneiss of the east side of Hoosac Mountain, which is 

 traceable into coarse conglomerate, " white gneiss," and 

 quartzite as we pass towards the north and west. The 

 lower part of the Hoosac schist passes similarly through 

 the calcareous schist of the Hoosac Tunnel into the 

 Stockbridge limestone. The upper part of this schist is 

 perhaps to be correlated with the Berkshire and Greylock 

 schist series, which are separated by the Bellowspipe 

 limestone. The rocks are over-folded and faulted as well 

 as metamorphosed, but patient mapping has unravelled 

 the complex structure, and enabled the writers to assign 

 the Stamford gneiss to the Pre-Cambrian System, the 

 Vermont Formation and the Lower Stockbridge limestone 

 to the Cambrian, and other rocks mentioned to the 

 Silurian System. Much credit is due to the authors, and 

 their assistants in the field, for such a careful and detailed 

 piece of work, in which everything has been subordinated 

 to the elucidation and presentation of the facts. 



Mr. T. Nelson Dale,^ in his account of the Renselaer 

 tjrit Plateau of New York, thinks that the grit occupies a 

 place (probably unconformably) above the Hudson 

 River shales, which are themselves equivalent to the 

 Berkshire schists, but in a less altered condition, and in 

 their turn rest on the Stockbridge limestone. The upper 

 part of this last rock, which is crystalline and contains 

 clastic grains of quartz and felspar, yields fossils of 

 Trenton, Chazy, and Calciferous age, but its lower part 

 represents much more ancient time, as it contains 

 Cambrian fossils, and is thought to be the equivalent of 

 the Olenellus limestone, which, further east, rests on 

 Archican rocks. 



The grit itself is a coarse graywacke containing some 

 secondary minerals, and interbedded with red slates and 

 phyllites. On the west side of the syncline it is underlain 

 Ijy shales and phyllites of the Hudson River group, which 

 pass towards the east into muscovite and chlorite schists 

 which contain ottrelite, tourmalme, and more rarely albite. 

 A map, coloured sections, some admirable photographs, 

 and figures of rock-structure, illustrate the paper, which 

 appears to be an excellent piece of minute stratigraphical 

 and petrological work. 



To the same author we owe an account of the structure 

 of the ridge between the Taconic and Green Mountains 

 in Vermont.^ This consists of an anticline of lower 

 Cambrian rocks overlain by Stockbridge limestone and 

 Berkshire schist. The anticline is broken by a "key- 

 stone" fault, a thrust-plane, and one or two minor dis- 

 turbances. Mr. Dale also gives another interpretation to 

 the structure of Monument Mountain^ differing from 

 those advanced by Dana. He regards it as a synclin- 

 orium somewhat disturbed by faulting. The rocks 

 involved are the Stockbridge limestone, the Berkshire 

 schist, quartzite, and Silurian rocks. 



Mr. A. Keith* gives an account of the Catoctin Belt, a 

 region which is roughly the mountain tract of Maryland 

 and Virginia, a geological continuation to the north-east 

 of the Appalachian flexure system. The lowest rocks are 

 relegated to the Algonkian System, and consist of a flow 

 of diabase lava, followed by others of quartz-porphyry and 

 andesite, and by intrusions of granite ; these, again, are 



1 Thirteenth Annu.il Report of the Geological Survey of the United 

 States, 1891-92. (1893.) 



2 Fourteenth Annual Report of the Geological Survey of the United .States, 

 1802-93. (1894.) 



3 I hid. 4 Ibid. 



succeeded by other diabase flows : the diabases are now 

 converted into the Catoctin schists. The overlying Cam- 

 brian rocks are divided into four, and the Silurian into 

 three, divisions. A map of the whole area is given, and, 

 in describing both igneous and sedimentary rocks, 

 smaller scale maps are used to show variations in com- 

 position and structure. Lines are drawn on these maps 

 through those points where a given band of rock has the 

 same thickness (isometric or isodiametric lines, as they 

 have been called), and by this means a very good idea of 

 variation in thickness is given. Fossils found in the 

 Cambrian rocks have been of the utmost use, not only in 

 indicating the general age of the rocks, but also in making 

 out the general succession, and in unravelling difficult 

 bits of stratigraphy. The upper part of the Shenandoah 

 limestone contains Silurian (.' Ordovician) fossils, but its 

 lower part yields lower Cambrian with some middle 

 Cambrian forms. Above the representative of the 

 Hudson River shales comes the Newark formation, of 

 Jura-Trias age, which contains dykes and sills of diabase. 

 The region underwent folding, thrusting, and metamor- 

 phism of Appalachian type before the Newark time, and 

 subsequently was tilted and faulted on the monoclinal 

 plan. It was planed down in Cretaceous times, and 

 reduced to a base-level before the Lafayette period ; cer- 

 tain portions which survived this second planing are 

 delineated in a map. An interesting comparison is 

 appended in which the amount of area planed down, and 

 the amount of rock removed by different phases of 

 denudation are used to obtain a rough estimate of the 

 time elapsing during different parts of the Tertiary 

 Period. This gives the following relative figures : — 

 Tertiary, 134 ; Early Pleistocene, i ; Late Pleistocene,^ ; 

 Recent, a small fraction. 



Mr. C. S. Prosser's Bulletin on the Devonian Rocks of 

 East Pennsylvania and New York * is an admirable piece 

 of detailed stratigraphy, in which the fossils have evi- 

 dently been carefully collected and identified from each 

 important horizon, so as to place on record a number of 

 facts that enable detailed comparison to be made with 

 the better-known sections of western and central New 

 York. About 8000 feet of rock are shown, of which 500 

 belong to the lower, 2200 to the middle, and 5300 to the 

 upper division of the system. The bulk of the fossils 

 are of marine type, but some land plants were discovered. 



In his paper on a Geological Reconnoissance in North- 

 west Wyoming, Mr. G. H. Eldridge^ gives a description 

 of the great anticline of the Big Horn Mountains and 

 the three basins lying east, west, and south of it respec- 

 tively. The rocks belong to the .\rchiEan, Cambrian, 

 Silurian, Carboniferous, Triassic Cretaceous, and Eocene 

 systems. The Palaeozoic rocks appear to be conformable 

 throughout, and there seems to be no break between 

 them and those of Mesozoic age until the summit of the 

 Laramie beds is reached ; several breaks occur in the 

 higher beds. Coal, a lignite of good quality, is found in 

 the Laramie terrane, oil in the anticlines of Trias and 

 Niobrara beds, building-stone everywhere, and gold in 

 the north part of the Big Horn Mountains. The hot 

 springs and agricultural qualities of the soils are de- 

 scribed, and useful analyses of forty coals are appended. 



An account of the economic geology of a portion of 

 the main Appalachian coal-basin, and of an outlier called 

 the Potomac field, is given by Mr. J. D. Weeks in the 

 fourteenth annual report.^ The chief coals are the Pitts- 

 burg seam of the Upper Productive Measures, the Upper 

 Freeport and Lower Kitanning seams of the Lower 

 Measures, and the New River and Flat Top seam of the 

 Pottsville conglomerate. .A description of the measures 

 and their coals is given, but some of the vertical sections 



1 Bulletin of the United States Geological Survey, No. 120. (1894.) 



2 lUd., No. 119. (1894.) 



3 Fourteenth Annual Report of the Geological Survey of the United 

 States, 1892-93. (1894.) 



NO. 1377, VOL. 53] 



