718 REVIEWS 
graceful and striking shapes, they were not the somber bodies we find 
them to be in the rocks, but formed the most delicately woven fabrics 
of glass, latticed vases, urns and cups of the rarest delicacy and 
beauty. ‘They must have been, when denuded of their sarcode, among 
the most exquisite structures of the past, as their descendants are of 
the present. Nothing, for example, could have surpassed the graceful 
filigreed chalice of Botryodictya ramosa, with its slender, tufted pedicel 
expanding above with a cup ornamented with pendant pouches.” 
In the list of genera and species, twenty-eight genera and one 
hundred and twenty eight species of these organisms are recognized, 
a great majority of them being here described for the first time. 
These descriptions of genera and species, with the introductory 
portion of the volume, fill two hundred quarto pages of text, and 
they are illustrated by seventy finely executed lithographic plates. 
Swe 
Geological Report on Isle Royale, Michigan. By ALFRED C. LANE. 
Geological Survey of Michigan, Vol. VI, Part I. Lansing, 
1898, pp. 1-281. 16 plates, 29 feunes, 13 tables, 
The report begins with a historical sketch of the mining opera- 
tions from pre-historic times to the present. This is followed by a 
description of the method of constructing cross sections of the 
country from drill records, and this by an account of the succession of 
rocks forming the island, involving a detailed statement of the rocks 
traversed by sixteen drill holes. The results are compared with 
Irving’s cross sections of Keweenaw Point, and the conclusion reached 
that there is represented on the Isle Royale practically the whole of the 
copper range as it exists from the Central mine to Portage Lake. 
A comparison is made with the Minnesota section with less definite 
results. 
The portion of the report of more general interest is that which 
treats of the grain of rocks, both the theoretical discussion and the 
application of the theory to the rocks under investigation. The dis- 
cussion opens with the consideration of conditions that affect cooling 
of molten magmas. Laws controlling the loss of heat are expressed 
mathematically, and diagrams are constructed exhibiting rates of 
cooling under various conditions. Deductions regarding the variations 
