86 
Transactions Texas Academy of Science. 
Comstock^ Theo. B. 
struetion of majps- 'Greologieal conclusions tentatively announced in the 
First Annual 'Report, mostly confirmed hy subsequent field work. Material 
■on hand. Fossils from the Cambrian, Silurian and possible Devonian. 
Minerals. Discovery of tin ore. Acknowledgments. 
32. 
Beport OR the G-eology and 'Mineral Eesonrees of the Central 
Mineral Begion of Texas, chiefly south of 'the San Saha river and 
north of the Pedernales river, ivest of Burnet and east of Menard- 
ville and Junction City. 
Second Ann. Bept. of the GleoL Surv. of Texas, 1890, pp. 553- 
664; 2 plates; 2 maps; 9 figures. Austin, 1891. 
“Skeleton: iPart d. — 'General Review of (Geologic Structure. Outline 
O'! the geologic groups, for the use of persons engaged in prospecting and 
development. Statement of the classification adotpted, with cha-rt showing 
the various terranes in chronologic order. General statement of the eco- 
nomic products of each main geologic horizon. Part ’ll. — Economic Geol- 
ogy. How to use the report for practical purposes. Plan of this part. 
Metalliferous Deposits. Precious Metals. Gold. — ^Possible sources stated, 
with results of assays, etc. ^Silver. — ^^Sources of supply. Districts limited 
and ores discussed- Rase Metals. Copper. — 'Belts defined, with descrip- 
tions of localities and cuts showing structure. Lead. — Districts outlined; 
outcrops illustrated 'and described. Review of the situation. Guide to pros- 
ipec'tors. Table I. Assays for gold, silver, copper, and lead. Tin. — ^Full 
discussion of the present situation, with cuts showing the geologic condi- 
tions where tin ore has been found; character of ore and mode of occur- 
rence. Uncertainty of discovering the mineral in commercially important 
quantities. Zinc. — Absence from this district- Unsuipported claims of dis- 
covery of zinc blende in 1890. Manganese. — ^Areas in which the ores out- 
crop. Belts defined. Diseussion of ores and modes of occurrence. Table 
III. Analyses. Iron. — Extent and importance of the ores of the district. 
Hints regarding the development of the iron fields. (Separation of the ores 
into five classes, individually discussed in detail, with location, description, 
and full treatment of the six great belts, or axes, including important hints 
concerning the mining of ores. Table III. Analyses of iron ores. Metal- 
lurgic review of iron fields. 'Probable future of the iron industry. 
Building 'Stones. Granites. — ''Seven classes, distribution and economic 
value. Marbles. — (Three classes, their distribution and uses., Limestones 
and Dolomites. — ^Localities and character of material. Sandstones, Slates, 
Schists, Clays, and materials for Cements, Lime, Mortars, etc. 
Refractory Materials. Fictile Material. Materials for Paints. 
Part III. — .Supplement. Additional notes on stratigraphic geology.” P. 
555. 
“The area of Pre-Carboniferous rocks comprising the Central Mineral 
Region, as defined in the Report of this ^Survey for 1889, was estimated at 
less than four thousand square miles. The more complete survey of 1890 
has materially extended the boundaries of the tract by the discovery of 
uncovered 'Silurian and Cambrian strata in extensive fields hitherto sup- 
