The Devonian crinoidal rocks in the Andrews South Devonian field, Andrews County, Texas, show a clear relationship between the original sediment and its diagenetic history. The limestone facies is composed of a supporting framework of crinoid fragments, interparticle lime mud, and rim cement. Laterally, it changes to dolomite, which was originally composed of a supporting framework of lime mud containing scattered crinoid fragments. The porosity in the limestone facies was formed by selective leaching of interparticle lime mud after the formation of rim cement. The porosity in the dolomite facies was formed during dolomitization and is generally related to the ratio of the lime mud to crinoid fragments; the dolomite samples with the highest porosities contain the highest amount of crinoid fragments.