Intrusive Relationship of the Granite to the Rhyolite (Porphyry) of Southeastern Missouri
Introduction Although the general distribution of the igneous rocks of southeastern Missouri has been known since the publication of Schoolcraft’s report, “Lead Mines of Missouri,” in 1819, they were first studied and mapped in detail by Erasmus Haworth about 70 years later. In one of his papers, published in 1888,1 he states that “a comparative study of the porphyries and granites of this district reveals the fact that there is no sharp division line between the two, at least, so far as can be judged from the hand specimens.” He further raised the question as to whether these rocks in Missouri illustrated “the gradual transition from a holocrystalline, coarse‐grained rock through the fine-grained ones to those which originally were vitrophyres.” He concluded, tentatively at that time, that such a gradation existed. Haworth’s next contribution was a paper2 in which he presented the arguments in favor of an Archean age and . . .