REPORTS OF GEOLOGISTS. XCV11 



the profiles taken by the topographer with the solar transit (Gurley's). The 

 large map has been constructed from the vertical and horizontal angles ob- 

 served along these lines at short intervals, the intervening topography having 

 been sketched in. In a few instances (over small areas which could not be 

 covered by our lines in the limited time allowed us), the topography has 

 been worked in from the sheets of the United States Geological Survey, but 

 in every case of this kind I have personally gone over the tracts and satisfied 

 myself that those portions of the sheets are reliable, or I have had the inac- 

 curacies corrected by special work with the compass. The result is a topo- 

 graphic map much more accurate than any hitherto published, and one which 

 is suited to the correct delineation of the geology as far as we have been able 

 to carry our studies. The monuments of the United States Geological Sur- 

 vey Geodetic Corps have been placed with precision, and these have furnished 

 valuable checks upon our work. The field notes, including the geology, 

 were all plotted first upon the scale of one thousand and forty feet to the 

 inch, reduced by pantograph to 62 | 00 , and this again reduced in the office 

 to yg-^nnj an( ^ carefully drawn for further reduction by photography, the 

 engraving being upon the scale of gxoWo" ? or tnree an d nine-tenths miles to 

 the inch. The geology was worked up in detail along the transit lines, which 

 were usually laid out with reference to the structure, and many complicated 

 areas were thus studied minutely. Contacts of the different terranes have 

 been instrumentally run as far as has been possible, and details of this char- 

 acter which can not be given from actual knowledge are shown upon the 

 map in broken or dotted lines. Subsidiary topography was also largely 

 worked out by the compass. 



The geologic conclusions tentatively announced by myself in the First 

 Annual Report are mostly confirmed by subsequent work in the field. 



Besides the results announced in my accompanying report, there remains a 

 large amount of partially elaborated material, and some which is in a more 

 advanced stage of preparation, but which could not be arranged and edited 

 in time to appear therewith. A series of thin slices of our crystalline rocks 

 is being made in the laboratory, and some exchanges with other workers 

 have given us a fair beginning in this department. 



The fossils obtained from the Cambrian, Silurian, and possible Devonian 

 strata have been given a preliminary examination, but little more can be done 

 with them until more complete collections can be secured. A table of the 

 minerals of my district, with ample notes of localities, modes of occurrence, 

 special characteristics and economic relations, is so far advanced that its pub- 

 lication as a Bulletin might be feasible at an early date. 



The recent discovery of tin ores by myself necessitated a special trip to 



Llano and Mason counties in November. With Mr. Ellsworth as assistant, I 

 7— geol. 



