Dodge.] 406 [February 3, 



were trilobites. A number of these have also been identified in North 

 Wales, and some in Sweden. 



Although these rocks may be regarded as of the earliest age in 

 which life under similar conditions to the present can, as yet, be 

 safely asserted to have existed, it seems extremely probable that 

 whole faunas, lasting through untold ages, preceded the earliest with 

 which we are acquainted. On this point, Mr. Hicks, who has done 

 more than any other man to reveal the abundance of the fauna of 

 these rocks in Wales, which were previously supposed to be barren of 

 life, says: " The earliest known brachiopods are apparently as perfect 

 as those which succeed them, and the trilobites are of the largest and 

 best developed types. The fact also that trilobites had attained their 

 maximum size at this period (Menevian), and that forms were present 

 representative of almost every stage in development, from the little 

 Agnostus with two rings to the thorax, and Microdiscus with four, 

 to Erinnys with twenty-four, and blind trilobites along with those 

 having the largest eyes, leads to the conclusion that, for these several 

 stages to have taken place, numerous previous faunas must have had 

 an existence, and, moreover, that even at this time in the history of 

 the globe, an enormous period had already elapsed since life first 

 dawned upon it. '* (Quart. Journ. Geol. Soc. Lond., xxviii, p. 174.) 



I remember to have heard our lamented Agassiz lay down the en- 

 couraging principle that where a single fossil has been found, an 

 abundant fauna may be expected. And there seems every reason to 

 believe that the rule will hold good in this vicinity, for metamorphic 

 influences have not so altered these slates as to obliterate their fossil 

 contents, however much these may often be obscured. 



In all probability these fossils will be discovered in many other 

 localities than at the single quarry at Braintree, when the similar 

 strata elsewhere are subjected to the same scrutiny. Indeed, it was 

 stated when this locality was first made known, that fragments of sim- 

 ilar trilobites had been found in erratics on George's Island, in Boston 

 Harbor. 1 We have seen that this island rests on a slate foundation, 

 and a few miles northward across the harbor (beneath which simi- 

 lar slates probably lie) we come upon outcrops of belt (a) above 

 described. 



The often quoted lingula in a slate pebble in conglomerate at Taun- 

 ton, again, indicates the existence, at some time, of early fossiliferous 

 slates at no great distance. 



i Proceedings Boston Soc. Nat. Hist. (1851), Vol. vi, p. 42. 



