Sequence of Rock Formation

"I am willing to admit mistakes and change my views when the evidence demands it." (Gentry, 1984, p. 92)

I confronted Gentry with the information about dikes by sending him some of the references and in subsequent phone conversations with him in February, March, and April of 1987. In a phone conversation on April 12 he told me that the sequence of events in the area was not what I told him it was, but that the intrusive rocks were first and the sedimentary rocks were last to form. What made him the most anxious were the stromatolitic horizons found just south of Bancroft in the marble units cut by the Faraday Gabbro and pegmatites. He challenged their very existence. This is a common creationist tactic - when confronted by problematical evidence, deny it. As can be seen from Figures 6 and 7 the stromatolites do indeed exist. There is no question as to their authenticity (M Easton, personal communication, September 1987).

I also explained to Gentry that there are features that show conclusively the sequence of rock formation from basaltic flows, 30 kilometers to the south near Madoc, followed in a complex way by the sedimentary rocks, succeeded by the intrusion of the gabbro plutons and finally the pegmatite intrusive [See Figure 16]. In fact, I collected samples from this very sequence and sent them to him with a description. During the course of the April 12th conversation, Gentry challenged that sequence by claiming it is not a vertical one, but that it covers a large horizontal distance. Even though I told him the sequence had been tilted on its side, he still did not appreciate the significance of the sequence.

(Photo right is from a road cut on Hwy 62 just south of Bancroft. Even though it has seen moderate metamorphism, bedding planes are clearly visible. Photo by J.R.Wakefield, 1987)

At one point I explained to Gentry that the nature of the intrusive rocks is clear and conclusive, and that, among other things, one can see where contact metamorphic recrystallization of the sedimentary rocks produced by the heat of the intrusive body has taken place. Gentry claimed that the recrystallization was not due to the molten intrusive rock but, since the intrusive rocks were first, was caused by some sort of chemical alteration of the sedimentary rocks.

I explained to him that the intrusive rocks, including the pegmatites, show little or no regional metamorphic alteration, whereas the surrounding sedimentary and volcanic rocks show many effects of having been metamorphosed. Thus, the intrusive rocks must have been emplaced after, or very near the end of the metamorphic event. I had to explain what regional metamorphism is, but Gentry simply refused to accept this idea.

I also described to Gentry still another conclusive evidence of intrusion. There are pieces of sedimentary rocks enclosed within the intrusive rocks, engulfed and surrounded by the melt. The descriptions (previously given) on the Faraday Mine includes some of these features and Figure 12 is a photo of a piece of pegmatite with an inclusion in it from the dump of the Faraday Mine. I asked Gentry how the inclusions got into the solid rock if the sedimentary rocks were younger than the intrusive rocks. Gentry simply denied the existence of the inclusions even though their occurrence is described in the literature I had already sent him. Furthermore, the inclusions are very common, and descriptions of them can be found throughout the geological literature of the Shield. Clearly, Gentry either has not read or does not understand this literature.

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