1869.] 177 {Jacksou. 



my friend, Eev. J. B. Percy, Assistant at the Museum in Cambridge 

 that these conglomerates closely resemble beds of this age in New 

 Hampshire, though I do not know that he agrees with me in this 

 opinion concerning their age. As Mr. Percy's acquaintance with the 

 primordial rocks of North America is more thorough than that of 

 any living geologist, we may hope from him some satisfactory ex- 

 planation concerning the precise position of these beds. 



No fossils have as yet been found in the conglomerate; careful 

 search may yet reveal something, however. It is to chance fossils and 

 to a careful study of the character of the pebbles composing the con- 

 glomerate, that we must look for a solution of this question of the 

 time of formation and conditions of deposition of this mass of beds. 



Dr. Charles T. Jackson asked Mr. Shaler whether he considered 

 greenstone porphyry to be a rock of igneous or aqueous origin. Mr. 

 Shaler said he regarded it as igneous. Dr. Jackson then said there 

 was an insensible passage of syenite into greenstone porphyry, as 

 may be seen in numerous localities in Cohasset and elsewhere, and if 

 one of these rocks is of igneous origin, the other must be also, of 

 course. He then entered into an analysis of Mr. Shaler's arguments, 

 and said that the obscurely stratified rocks on the borders of the 

 great mass of syenite at Quincy, proved the igneous influence of the 

 erupted syenite upon the upturned strata which it had elevated by its 

 protrusion. 



It is very common to find numerous fragments of stratified rocks 

 through which syenite or granite has been protruded, mixed with 

 the mass of injected rock. He had recorded a great number of such 

 cases in his State Geological Reports; and Prof. Hitchcock had also 

 observed them. Now these torn up fragments appear to be imbedded 

 in the masses of syenite or granite, exactly as they are in trap and lava 

 dykes, which burst through stratified rocks, and bear up the broken 

 pieces imbedded in their paste, and there is every analogy between 

 greenstone trap rocks, porphyries, syenites and granites, indicating 

 for them all a formation by igneous fusion and elevation from below. 



He did not deny the powerful influence of super-heated water on 

 these igneous rocks, and referred to the researches of M. A. Daubree 

 on the formation of crystallized minerals in super-heated and strongly 

 compressed water; but the water, in aiding metamorphosis of min- 

 erals, was only a helping agent; fire was the chief cause of the 

 changes. (See Scrope on Volcanic Phenomena, and Daubree's Work 



X J ROCEEDI^G3 Ti. S. N. H— VOL. XTII. 12 JANUARY, 1870. 



