56 The American Geologist. .lan. isgo 
gneisses indicate, according to Dr. Lawson, that the.v are plutonic 
Tocks wliieli have crystallized sloAvly, probably under an extremely 
gradual diminition of temperature, from a thickly viscid, coherent or 
tough, hydrothermal magma. Up to the time of its final solidification, 
when it became approximately rigid, it appears to have been subjected 
to differential pressures, which, by causing a yielding or deformation, 
induced a flow in the mass, with the results of its foliation as gneiss 
and the parallel alignment of inclusions of foreign rock imbedded in it. 
Parts of the overlying Coutchiching or Keewatin series may also 
have been involved in the fusion of the Laurentian floor, becoming 
thus indistinguishable from it. Above the upper limit of fusion these 
overlying beds are supposed to have retained their stratification and 
to have rested as a crust of hard and brittle rocks upon the magma, 
subject to its metamorphosing influences. Fragments of the upper 
Archgean schists sank into the molten Laurentian, often to great dis- 
tances from the contact, and the fissures and crevices of the schists 
were filled with injections of this magma, which crystallized eventu- 
ally as the Laurentian gneisses, attaining its present rock structure 
later than the overlying series. In mapping these systems, it is dis- 
covered that the Laurentian gneisses and granite occupy large round- 
ish areas, isolated by encircling belts of the upper schists, much as the 
Archaean rocks of New Hampshire were mapped by Prof. C. H. Hitch- 
cock in the geological survey of that state. 
Drift is spread thickly over the country southwest of the Lake of the 
Woods and Eainy lake, but on the north and northeast it is scanty, 
and the bed-rocks have been everywhere rounded, grooved and pol- 
ished by the ice-sheet, the average direction of its movement being 
S. 40° W. The distribution and character of the drift deposits are 
explained in part by the former presence of the glacial lake Agassiz, 
held in on its northeast side by the barrier of the receding ice. 
Abundant rock-outcrops and intervening swamps render the greater 
part of the region unfit for agriculture, excepting a tract about fifteen 
miles wide along the Rainy river. 
Metamorphism of 7'ochs. A. Irving. Longmans, Green & Co., Lon- 
don and New York. 8vo. pp. 137. 1889. 
In this decidedly technical and learned treatise the author starts out 
by stating the exact points to be investigated, the difficulties of present 
theories and the inadequacy of the term "metamorphism" to convey 
a definite idea of any particular change in rocks. He uses the term 
metamorphism to indicate "only changes in the internal structure of 
rock-masses (i. e., in their morphology)," while changes in the exter- 
nal form and chemical changes, are denoted by the terms, Metatropy, 
Paramorphism and Metataxis. He defines them as follows: "1. Par- 
amorphism, including all those changes within a rock-mass, essentially 
of the nature of chemical changes in which the original minerals have 
had their chemical composition more or less altered, while new miner- 
als are formed within the mass. 2. Metatropy, or changes in the 
