Review of Recent Geological Literature. 329 
constituted so rich a field of petrographic inquiry within the last few 
years. 
Contact phenomena occupy a place of prominence in the study — For 
instance, Lacroix describes (p. 58 et seq.) in detail all the steps in the 
metamorphism of an argilaceous quartzyte (argile siliceuse) to a 
rock containing none of the original clastic minerals, and having a 
chemical composition corresponding to that of a possible igneous rock 
belonging to the family of the metamorphosing eruptive. 
It is interesting to note that while the author does not anywhere 
distinctly state his views upon the question of differentiation, he seems 
to accept neither the extreme view of certain French petrographers 
who reject the theory in toto, nor the other extreme exemplified by cer- 
tain German and American writers who would seemingly make of the 
theory a panacea for all the troubles of the student of petrogeny. La- 
croix's position is perhaps partially revealed by the useful distinction 
he draws between varying facies (faices dc variation) of an eruptive 
magma and a true petrographic series. By the former he signifies the 
diverse petrographic types resulting from the heterogeneity of the 
rocks produced by the solidification of a given magma when they have 
no geologic individuality (as of dikes, sheets, etc.,) distinct from that 
of the main magma. If, however, these diverse petrographic types play 
a geologic role distinct from that of the normal rock, they together 
constitute a petrographic series. He is careful to add that these distinc- 
tions are independent of all theoretical explanations of the cause which 
has produced the rocks in question. 
The conclusion of this publication will be eagerly awaited by all 
those interested in the advancement of petrography. a-, n. \v. 
The Clays and Clay Industries of Wisconsin. By Ernest 'Robertson 
Buckley. Bulletin No. 7, Part I (Economic Series, No. 4), Wis- 
consin Geological and Natural History Survey, E. A. Birge, Di- 
rector. Pages 304, with 55 plates. Madison, Wis., 1901. 
This report describes the clay deposits of Wisconsin, its 190 brick 
and drain tile factories, their methods of manufacture, and the eco- 
nomic conditions relating to the marketing of their products. The 
state has unlimited quantities of clay suitable for common building 
brick, terra cotta, fire proofing, drain tile, and earthenware. It is 
believed that other clay beds of less extent may be utilized for orna- 
mental building brick, paving brick and vitrified wares, and a fair 
quality of fire brick. Very plastic white kaolin occurs at numerous 
localities in Dunn and St. Croix counties, which is found to be well 
adapted for the manufacture of the highest grades of porcelain. It is 
largely used now, but almost exclusively for mixing with wood-pulp 
in paper-making. 
The extensive and thick clay formations adjoining lakes Superior and 
Michigan, which are regarded by the author as chiefly or largely of 
lacustrine or estuarine deposition, seem to the reviewer to be more 
properly classed, for the greater part, as boulder clay or till, deposited 
■directly from the ice-sheet, without transportation by water, and only 
