Geology and Mineralogy. 467 



great mountains of igneous rock form the dominating features of 

 topographic relief and express the geologic relations. The 

 formations are described and also the local geology of the various 

 districts is given in detail and several features of general interest 

 in structural and dynamical geology, particularly with reference 

 to the intrusion of laccoliths are brought out. 



The ores are found chiefly in two districts ; at Barker where 

 they are of the type of silver-lead ores occurring in limestones at 

 the contact of intrusive igneous masses, and at jSTeihart where 

 intrusions of diorite and other rocks have occurred in the 

 Archean complex. At this place the ores occur in a well defined 

 vein system and are gold and silver, the latter occurring in the 

 sulphides, ruby silver, polybasite, etc. The important mines, 

 their ores and workings are described. 



The petrographical report contains a full description of the 

 igneous rocks which are chiefly porphyries of several kinds, 

 granite, syenite and dioi'ite porphyries with intermediate types. 

 At Yogo peak is a differentiated mass changing from granite 

 porphyry through monzonites to shonkinite. The intruded 

 sheets and dikes present several rock varieties, the most interest- 

 ing of which are the minettes and analcite basalts.. Of all these 

 types detailed analyses by W. F. Hillebrand and H. N. Stokes 

 are given and in the theoretical discussion of the rocks of the 

 district are used to show that all of the main types are so related 

 to one another in a rock series that anyone of them may be 

 expressed in terms of the others; these relations being shown by 

 a diagram in graphic form. l. v. p. 



2. Iowa Geological Survey, Vol. X. Annual Report, 1899, 

 with accompanying papers. Samuel Calvin, State Geologist, 

 H. F. Bain, Assistant State Geologist. Pp. 1-166, plates i-xi, 

 figures 1-102, and 10 folded maps, 1900. — The Geological Board 

 of the State of Iowa is to be congratulated both upon the 

 admirable organization of its geological workers and upon the 

 equally admirable results it is annually producing. The board is 

 constituted of the governor, the auditor of State, two college 

 presidents and the president of the Iowa Academy of Sciences, 

 thus combining for effective service the forces of politics, educa- 

 tion and science. The geological staff for the year, besides the 

 geologist and assistant geologist, is drawn from the officers of six 

 of the colleges of the State and one high school and one from the 

 Chicago University. The papers of the present volume are 

 chiefly connected with the detailed mapping of the geology of 

 counties not previously so mapped. Forty-two counties in all 

 have been mapped, eight of them having been completed within 

 the year. The great value of the topographical sheets prepared 

 by the FT. S. Geological Survey is acknowledged, particularly in 

 respect to the Dubuque region, the important lead mines of 

 which are scientifically described in the chapter on Dubuque 

 County, prepared by the geologist and assistant geologist. 



Mr. Frank Wilder brings to notice, the fact " that the Hawarden 



