TACONIC QUESTION IN GEOLOGY. 149 



masses, it may be repeated that " the resemblance between primitive crystalline rocks 

 and what we know to be detrital rocks compressed, recemented, and often exhibiting in- 

 terstitial minerals of secondary origin, is too slight and superficial to deceive the critical 

 student in lithology, and disappears itnder microscopical investigation." '^^ 



§ 194. We haA^e already elsewhere in this essay (§ 135) referred to the local develop- 

 ment of crystalline silicates in sedimentary rocks by infiltration, and have, in another place 

 considered the relation of such a process to the question of the origin of primitive crys- 

 talline rocks. These we believe to have been formed anterior to the existence of detrital 

 sediments, and by a process which excludes alike all so-called metamorphic, metasomatic, 

 and plutonic hypotheses of their origin. At the same time we reject the Wernerian or 

 chaotic hypothesis, and its modification by Delabeche and Daubrée, which we have called 

 thermochaotic, in favor of a new aqueous or neptunian hypothesis, which supposes the 

 elements of these I'ocks to have been dissolved, and brovight to the surface from a disinte- 

 grated layer of igneous basic rock, the superficial and last-solidified portion of a cooling 

 globe, through the action of circulating waters. The soluble and insoluble products of 

 the subaerial decay, alike of igneous and aqueous rocks, are, however, supposed to have 

 intervened in the process, especially during the period of the later crystalline or Transition 

 rocks. This explanation of their genesis we have elsewhere proposed, and discussed at 

 length in a recent essay on " The Origin of Crystalline Eocks," ^^ and, in allusion to their 

 production through the intervention of sjirings, have called it the crenitic hypothesis. 



IX. Conclusions. 



§ 195. The task attempted in the preceding chapters, of discussing the history of the 

 Taconic Question, has involved a review of much of the work done in American geology 

 for more than sixty years, going back to the labors of Eaton, and even to those of Maclure. 

 Of the somewhat extensive literature '" of the subject I have made use, so far as has seemed 

 of importance in the controA'ersies which have arisen on this c[uestion, and have supple- 

 mented the researches of various investigators by personal observations extending 

 over a wider field and a greater number of years than those of any of my predecessors. 

 From all of these sources, I have here sought to bring together whatever has appeared to 

 be of value for the elucidation of the important problems before us. In the following- 

 sections, the conclusions which have already been set forth at length are summed up. 



§ 196. There exists in eastern North America a great group of stratified rocks, consist- 

 ing of quartzites, limestones, argillites and soft crystalline schists, which have together a 

 thickness of 4,000 feet or more, and are found resting uuconformably upon various more 

 ancient crystalline rocks, from the Laurentian to the Montalban inclusive. This series, called 



"* Trans. Roy. Soo. Canada, vol. ii, sec. iii, p. 23. 



™ Trans. Roy. See. Canada, vol. ii, sec. iii, pp. 1-67, and in abstract in Nature for July 3, 1884, p. 227, and 

 Amer. Jour. Science, July, 1884, p. 72. 



*" Dana, in the Amer. Jour. Science for 1880, xix, 163, has given " a list of the principaVpapers " on the Taconic 

 System, in which, while professing to bring together those adverse to the pre-Cambrian age of the Taconian, he 

 omits all reference to the opinions of Adams, of Ed. Hitchcock, and the later conclusions of W. B. Rogers as to the 

 (Upper) Silurian or Devonian age of the Taconian limestones. The list is in other respects very incomplete and 

 calculated to mislead the student. 



