284 Progress in Science. [April, 
Part III. discussed the origin of the Skiddaw granite from points of view fur- 
nished by field, microscopic, and chemical investigation. The gradual transi- 
tion from unaltered Skiddaw slate to mica-schist was proved under these three 
heads, while at the same time the abrupt passage from the mica-schist to the 
granite appeared to negative the idea of the next step, into granite, necessarily 
following in this case. In Part IV. the quartz felsite of St. John’s and the 
syenitic granite of Buttermere and Ennerdale were examined as to their 
origin ; and there was found to be much evidence in favour of their representing 
transition beds between the volcanic series and Skiddaw slates, metamorphosed 
in situ. The interesting rocks of Carrock Fell were then considered, and 
field, microscopic, and chemical evidence were all thought to lead to the in- 
ference that these masses of felsitic, dioritic (?), and hypersthenitic rocks were 
due to the metamorphism in situ of the beds forming the lower part of the 
volcanic series. In Part V. the author points out several considerations 
relating to metamorphism, to which the geological faCts of this district seem 
to lead. It would, he says, be “ unwise to suppose that every granitic mass 
has been the root and origin of some past series of volcanic phenomena ; for 
it may represent (1) a mass so deeply formed that, notwithstanding all the 
elevation and contortion produced by the intense pressure, no point of suffi- 
cient weakness was found whereby relief might be obtained and a volcanic 
centre be established ; (2) a mass which, though very deeply formed, was yet 
able to penetrate upwards for a certain distance along some area or line of 
weakness, though its final point of consolidation was still far below the sur- 
face, with which it forever remained unconnected by any volcanic neck; or 
(3) it may actually represent the very foundation of a true volcanic neck.” 
The author also treats of what he terms “ selective metamorphism,” and con- 
cludes his memoir by summarising the principal conditions under which rocks 
occur with regard to metamorphism : — (1.) That state in which igneous fusion 
is the most important or conspicuous element. (2) A state of aqueo-igneous 
fusion, occurring at a much greater depth than the last, and reaching only a 
dull red-heat as a maximum. (3.) A state in which the rocks are permeated 
by water at a considerably lower temperature than 400° C. 
A useful, descriptive, Catalogue of Rocks, Minerals, and Fossils, illustrative 
of the Geology, Mineralogy, and Mining Resources of Victoria, has been pre- 
pared by Mr. R. Brough Smyth, F.G.S., F.L.S., Secretary for Mines and Chief 
Inspector of Mines for the Colony. 
We have received No. 6 of the Second Series of the “ Bulletin of the 
United States Geological and Geographical Survey of the Territories,” by 
Mr. F. V. Hayden, U.S. Geologist in charge. The Bulletin of the Survey 
was commenced in 1874, for the purpose of giving to the world, more rapidly 
than through the Annual Reports, the vast amount of new material which was 
constantly accumulating under the auspices of the Survey. The success at- 
tending the publication was so great that it commenced the year 1875 as a 
regular serial, and six numbers have been issued of about five hundred closely- 
printed oCtavo pages, with twenty-six pages of maps, sections, and other illus- 
trations, with table of contents and full index. 
Microscopy.— -A new form of single magnifier has recently been contrived 
by Mr. John Browning. It is thus described by the inventor: — “The platy- 
scopic lens is a triple achromatic combination, in which the chromatic and 
spherical aberrations are corrected by a central lens of dense glass. This lens 
is nearly three times as thick as the crown-glass lenses. The interior curves 
are almost hemispheres. The final correction for spherical aberration is made 
by altering the thickness of the dense glass lens. The three lenses are united 
by a transparent cement which has a refractive index corresponding very nearly 
with that of glass. This prevents light being lost by reflection from the surface 
of the deep curves. The platyscopic lens is made of three degrees of power, 
magnifying respectively 15, 20, and 30 diameters.” Microscopists who have 
occasionally employed a low-power achromatic objective as a hand magnifier 
