PKTUOOUAPHIC RI<]P01iT ON ItOCKS FROM TIIK; UNITED 

 STATES-MEXKM) liOlINDAIfV. 



liy Edwin C. E. Lord, IMi. 1). 



Tlie mateiiiil upon which this report is based was colhicted by 

 Dr. E. A. Mearns, of tlie International Hoiin^hiry (Join mission, and 

 deposited by him in the \J. S. National Museum.' 



The method used in eolleotin^;' the rock specimens may be brieHy 

 described as follows: 



IJeginniuf^ at a point on tlie Uio (Jrsinde about .'{ miles above 101 Paso, 

 Texas, the line of survey extended across the continent, a distance of 

 more than 725 miles, through a geologically unexplored country. At 

 certain monument stations along the route special halts were made for 

 the purpose of collecting and shipping s[)e('imens of scientific; value. 

 Only those monument stations, however, in the immediate vicinity of 

 which petrographic material was obtained, have been given on the 

 map.- 



Owing to tlie rapid jirogress of the 8urv<'y these halting places were 

 frequently far apart and the g(H)logic data obtained of a very frag- 

 mentary nature. In view of these facts it has been found necessary to 

 treat the subject exclusively from a ])etrographi('al standpoint and 

 describe the rock in petrograjdiic groups without regard to their 

 geological relationship. 



The geogra])hi(;al order of occurrence, howe\'er, h;is been strictly 

 nuiintained in each group, and the monument numbers (Mon. Nos.) 

 attached to each locality can be readily found on the map. The speci- 

 men numbers ai)pear in parentheses. 



'Tlie Hpecimens were iiccoiiipaiiied I>y iiiiiiiy field notes. TlieHf, and a Hinall Hiuile 

 niaj) of tli<5 bonndaiy lino, ])repar<-(l especially by Dr. Mearns, have Iteon of j^reat 

 valn(! to the anthor, who also wishes to exjne.ss his iinhihtedness to I'rol". (I. P. 

 Merrill, head cnrator departmcint of K''"loffy, for the many i)rivilef?cM a<!corded him 

 in the Mnsenm. 



-For Mxorr exact data, concerning the topography of the country tiie reader is 

 referred to the large scale djoiiVon) topographic ma)) of the boundary line soon to 

 appear with the report of the commissioners nnder the anspices of the State 

 Department. 



Proceedings U. S. National Museum, Vol. XXI- No. 1 173. 



773 



