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CONTftIDUTIONS TO ECONOMIC GEOLOGY s metnmorph~country rock adheres to the dikes. The dikes e from microgrnnrte and granite porphyry to olivine gnbbro Irophyre. he distribution of dikes in the Trinidnd caul rely suggests the eats of at ]east five superimposed groups or swarms. The most epicnou9 is the swarm that is radial from }Vest Spanish Penk. greatest concentration of dikes in this swarm is west of lyest tnish Penk where they are generally short. The dikes rarely coda the metamorphosed uppermost beds of the Iluerfnno(?) fot•- tion, These dikes range from micrograuite and granite porphyry gabbto lnmpraphyto and basalt. A second system of dikes h•ausects those that radiate from }vest Walsh Yenk. This system is made np of subpnrnllet dikes that Ike from N. 60° F. in the nm•thern part of the field to N. SG° )/.' the southern part. llikes of this system crop out from about 37°10' 37°40' north latitude. The trend of the dikes is normal to the nernl trend of the folded sedimentary tacks. Dikes of this system e the longest within the coal field; they range in length trom 2 to most 14 miles. These dikes range from syenite porphyry and min'ophyre to of ivine gnbbro lamprophyre. The s,vnrm that is radial frmn Dike Nfotmtnin 20 miles uortlnvest f }Pest Spanish Penk is another conspicuous system. 1.ikc the 'crest Spanish Penk system, the dikes rndinting to the west are shorter r+an those rndinting fo the east. 1'he longest dikes extend enst- tortheastn•nrd to within n few hundred feet. of the intrusive moss hat makes np the Black Ril{s. 'Phe dike rocks are similar to tlwse tt Dike 11(ountnin and the i3inck Tiills, and at•e fncies of syenodiorile. A large dike of microsyenodiorite southwest of lVnlseuburg extends across the eastern part of the coal field in nn east-,rest direction. It. s generally nrcunta in plan and coarnve t.owm•d the sontl+. The ;talks varies from N. A3° L. nt. its western uxtren+ity to N. Ati° 1P, tt its east ern extrem it.y. Throughout the Trinidnd coal field thm•e are many isolated single or stnnil sets of basaltic and ]nmprnphyric dikes that. show no ap- parent pattern ot• gm,e+:~l nssocintions with the L•u~ge dike systems m• other types of intrusions. The dikes m•e thin mxl short. SILLS Basalt, gnbbro Inmprophyt•e, and micros}•ennslim•ite sills intrude the sedimentary rocks of the Trinidad s;uxlstone, Vermejo formation, and Raton fm•matiou ns well ns the bads of tha 11uerFum(?) ku•mn- tion near rho lyest. Spanish Peak stock. Sills are most abundant. and extensive in the eastern part of the coal field from Ltt.iNUle :17°30' RE60URCE9 OF TRINIDAD CUAC r,au.., • north sauthwnrd to the Intitade of Trinidnd and the drni~t of thn Purgntoire Riyet• to n point nhont n mile ,test of }Veston. here are few sills in the coal field north of the Cuchnrn River, and the}• ntr uncommon or absent in the Trinidnd sandstone, Vermejo formation, and Raton formation along the western mnrfiin of thecoal field. Several d+kes rndinting northwestward from 1Vest Spnuish Penk are apparently parallel to the strike of strata in tl,e Poison Canyon and Cuchnrn formations crest of the Cuchnrn River, and seem to be sills in this Wren. Although the sedimentary beds nt•esteeply dippinfi nt 25° to 51°, rho dikes nr•e nearly rerticnl, mtd probably cat ncrosG the beds below the surface. Only two sills, except for those intruding the metamorphosed beds of the Huerfnno (?) formation adjacent to the 1Vest. Spanish Peak stock, intrude ns high in the strntigtnphic sequence ns the Poison Canyon formation, and theso are in the lowermost beds of the Poison Canyon south of the South Fork of the Purgntoire River about 2 miles east of Torcio and southwest. of Morley. Ifnopf (193G, p. 177•(} reported a sill of microgcnnite 20 feet. thick near the Spanish Peaks on the upper rcvtches of the South Fork of Truj illo Creek. The sills in the Trinidad coal field are commonly complex m• nn,l- tiple intr•llsions that have invaded the shnly or cooly units of the Upper Cretaceous and Tertiary fo+•mntions. They are generally more resistant than the shale or coal and commonly fat•rn strike ridges and ledges, T1,ey generally are not thick indi,•idunl sheets, but are made up of nnnstomosing stringers of ig»eous rocks that seem to be con- cenirnted in nnrro,v zmtes. Some of tho sills seem to cut across bedding, but. poor exposures make determination of the exact relations di0icult. Near Snutn Clnn1 Creek and south to Trinidad, sills are connected n•ith dikes at se,•e,:21 places. These dikes are litholo~~ically similar to the sills. They are pert of the dike systems that strike in n renernl east-west direction ncrnss the cant field, n+sd cut the s,cnrtn radiating fi•on Nest Spnuish Penk. The sill rock is dark gray and fine grained. Away from Heir cmt- tncts u•it.h the intruded rocks some of the thicker sills :u•e coarse l;rnined with rliabnsic texture. The sills rnn~•e in thickness from n fe,r inches to 40 feet, and extend over several sgnnre mites. QEOLOQIC STRUCTURE The principal structural feature of the Trinidad soul field is the Rohm basin, which is n broml nsynuuetrical (rough whose axis trends generally unrUrn-urd ft•am near Ute Pnrk, N. ll(ea., into Iluerfnno Park, Colo. The Cnlo•ado part of the trough has been named the La Vets syncline (.Tnhnson and Stephens, IA54n; }food, .lohnson, and