Review of the New York Geological Reports. 149 



• 

 Here, then, appears to be an unequivocal instance of the exist- 

 ence of graphite in an altered protozoic limestone of aqueous ori- 

 gin ; and the graphite is in greatest abundance, not in the imme- 

 diate vicinity of the dyke, where the heat must have been most in- 

 tense, as we should expect from the inferences of Prof. Emmons, 

 but in the altered parts of the limestone more remote from the 

 centre of igneous action. 



The Taconic rOcks are supposed by Dr. E. to be the equivalent 

 of the lower Cambrian of Prof. Sedgwick. It will appear how- 

 ever, in the following extracts from Mr. Murchison's address, de- 

 livered at the anniversary meeting of the Geological Society of 

 London, February 17th, 1843, that the Cambrian formation is 

 now no longer recognized as a distinct system. Speaking of 

 the palaeozoic rocks of the British isles, we find on pages 16 and 

 17, the following remarks : — " Prof. Sedgwick has reassured him- 

 self that there are fossiliferous slaty masses of great vertical thick- 

 ness, which rise out from beneath lowest Silurian rocks of North 

 Wales hitherto described, and occupying the region of Merion- 

 ethshire and Snowdon, alternately rest upon chloritic and mica- 

 ceous schists (Menai Straits), into which they do not pass. The 

 lowest of these fossil bands, forming the summits and flanks of 

 Mod Hebog and Snowdonia are, he conceives, several thousand 

 feet below the Bala limestone. 



" The hope, however, which was entertained by my friend of 

 finding these vastly expanded and lower members characterized 

 by peculiar groups of fossils, has been frustrated, and whatever 

 may be the thickness of this lowest palaeozoic division, in which 

 he has collected a great number of species, he now fully admits, 

 that zoologically it is from top to bottom, a lower Silurian series. 

 Charged as it is with characteristic Orthidse and trilobites, inclu- 

 ding the Asaphus tyrannus, so characteristic of the lowest Silurian 

 rock, there are, as may be expected, a few new and undescribed 

 species : and, among these, an Ophiura will not appear the least 

 extraordinary. 



" The base of the palaeozoic deposites, as founded on the dis- 

 tinction of organic remains, may now, therefore, be considered 

 to be firmly established ; for the lower Silurian type is thus shown 

 by Prof. Sedgwick himself to be the oldest which can be de- 

 tected in North Wales, the country of all others in Europe, in 

 which there is a great development of the inferior strata." 



