500 Frof. T. McKenny Hughes — Brecciated Archcean Rock. 



Huronian, there are not wanting portions of its more schistose 

 strata which have a resemblance to certain Montalban rocks. Hence 

 it was that at an early period in the writer's studies he attempted to 

 group Montalban and Taconian under the name (soon after abandoned) 

 of Terranovan. For a detailed account of the whole Taconic con- 

 troversy, see the author's Mineral Physiology and Physiogi'apJiy, and 

 for a more concise statement, but with more new light, " The 

 Taconic Question Restated " in the American Naturalist for 1887. 



13. The name of Taconian was given to the Lower Taconic of 

 Emmons to distinguish it from his Upper Taconic, which is essentially 

 uncrystalline, and, as shown by its trilobitic fauna, and recognized by 

 Emmons himself, is clearly Cambrian, and is in some regions directly 

 overlaid by Ordovician strata. Beneath the recognized Cambrian, ia 

 parts of the North American continent, is a great body of uncrystalline 

 sediments, which I have designated Keweenian. While newer than 

 the Taconian, their relation to the unconformably overlying Cambrian 

 is as yet uncertain. 



It is not claimed that the above indicated division of the great 

 pre-Palgeozoic or Archeean succession is complete. Further study will 

 probably show that there are other groups, and furnish grounds for 

 subdividing those here proposed. They are, with small help from 

 without, chiefly from the generalizations of a single observer during 

 a period of forty years, and as such are offered as a first attempt at a 

 classification of the stratified crenitic rocks, and as illustrations of 

 the process of mineralogical evolution. It must be remembered 

 that for reasons already assigned (§2), none of these groups save 

 the fundamental granite can be supposed to possess the characters 

 of uniformity and universality. 



IV. — On Some Beecciated Eock in the Arch^an of Malvern. 



By T. M'Kenny Hughes, M.A., F.G.S., 



"Woodwardian Professor, Cambridge. 



THE question of the origin of the Archeean rocks is one of such 

 great interest that it will not be thought imimportant on the 

 one hand to record any facts that may bear upon it, and on the other 

 to examine somewhat severely all the evidence that may be from 

 time to time brought forward on the subject. Among the facts 

 which may be adduced in support of the view that the Archaean 

 rocks are altered sedimentary strata, the occurrence of breccias and 

 conglomerates may well claim a foi'emost place ; and a vast amount 

 of superincumbent theory must rest on a very shaky foundation if 

 there be any doubt whether some of those ancient fragmental beds 

 be true conglomerates or not. The manner of occurrence, the mode 

 of formation, and the character of pseudo-breccias and pseudo- 

 conglomerates become therefore questions of first importance. 



What one would be at first inclined to accept as evidence of 

 the conglomeratic character of a bed would be that the included 

 fragments were rounded, and that they were of a different character 

 from the mass in which they were imbedded. I have on a former 



