EARLY DEVONIC HISTORY OF NEW YORK AND EASTERN NORTH AMERICA 



72> 



P h a c o p s primaeviis; t The extra-siitural part of the 

 ctplialoii, 2 the cranidium, 3 pygidiiim, 4 a compressed 

 glabclhi showing tfie PteryKometopiis-like lateral lobes, 5 

 underside of doublure showing lateral crenulations. All 

 figures enlarged 



Botli cephaloii and pyg^idium, which occur commonly in these slabs, 

 present an almost mature development of the genus Phacops, such as we 

 have heretofore expected to find j 



only in rocks of Devonic age. The 

 glabella when uncompressed is round 

 and full without segmentation but 

 when compressed the lobes and fur- 

 rows appear and the glabella takes 

 on the aspect of a Pterygometopus. 

 The suture is high on the cheeks and 

 the eyes relatively long but with low 

 visual surface. The cheeks are with- 

 out spines. On the under surface the 

 doublure is grooved and crenulated 

 as in the early Devonic species. The 

 pygidium is very short, having no 

 resemblance to the. dalmanitiform 

 plate of Pter\-gometopus, has a stout spindle which ends abruptly and carries 

 3-4 annulations while the pleurae carry 2-3 flat ribs each divided by a fine 

 furrow. In a preliminary account of the geology of Perce' I noted that 

 these structures indicate a close approach to Phacops 1 oga n i and con- 

 cluded that the species probably indicated a late stage of the Siluric. The 

 additional material since acquired leaves little doubt of the Trenton age of 

 these beds notwithstanding the apparentl)' much later age of this trilobite 

 as interpreted by prexiously recognized standards. 



The Cape Blanc limestones" thus appear, from tlie evidence before us, 



to represent essentially the same time inter\al as the Siluric series displayed 



on the shore from Cape Canon to the head of Mt Joli ; furthermore, though 



these series differ in the lithic characters exposed, there is every reason to 



regard the former as a downthrown part of the south limb of the great 



Perce fold. This mass of limestones fronting the sea at Cape Blanc extends 



inward in a broad band throusfh Irishtown and its eastern ed<je has been 



traced by the writer through the Perce mountain where it nearly abuts 



ao-ainst the o^reat fault front of the Bonaventure cono-lomerate known as 



the " Amphitheater." From here it bears off towards the south shore of 



Malbay and disappears at the south end of Corner of the Beach, not reach- 



' Perce. A Sketch of its Geology. N. Y. State Paleontol. An. Rep't 1903. 1904. 



p. 163. 



