308 Geological Society : Prof. Setlgwick on the 



generally ill preserved ; but among them are some corals that are 

 common both to the Silurian and Cambrian systems. The fossils of 

 New Quay and South Petherwin are an exception to the remark ; as 

 many of them are well preserved. They consist of corals ; encri- 

 nites ; numerous specimens of the genera Terehratula, Orthis, and Spi- 

 rifer; of four or five species of OrfAocer«ii7es; Goniatites; and lastly, 

 three or four new species of a genus described by Count Munster 

 under the name Clymene, and by Mr. Ansted under the name En- 

 dosiphonites. As they occupy a position so much lower, so, as a 

 group, these fossils are distinct from those of the Silurian system. 



Conclusion. — The author here takes a retrospect of the preceding 

 description, and states that the classifications are founded on the 

 details of actual sections ; and that as far as such detailed sections 

 throw light on the several questions that may arise, there is not 

 much that remains to be done in England. Some of the generali- 

 zations are, however, founded on imperfect evidence ; and to render 

 them more complete, it is now necessary to appeal to the organic 

 remains in the several groups. In this department little has been 

 yet effected, excepting in the higher part of the Silurian system, 

 where the upper divisions (at least in one part of the island) assume 

 definite mineralogical and zoological types. Whether definite zoolo-^ 

 gical groups can be made out in any lower system still remains to 

 be seen. The rigid determination of the Devon and Cornish fossils, 

 which are very numerous, and a rigid comparison of the Berwyn and 

 Bala fossils with those near the base of the third group of the Cum- 

 brian section, give the fairest promise of an answer to the question, 

 and are pointed out as immediate desiderata. 



The difficulty of classification by organic remains increases as we 

 descend, and is at length insurmountable ; for in the lowest strati- 

 fied groups, independently of metamorphic structure, all traces of 

 fossils gradually vanish; and the great range of certain species 

 through numerous successive groups, and the very irregular distri- 

 bution of fossils even in some of the more fossiliferous divisions, add 

 greatly to the difficulties of establishing true definite groups even 

 within the limits of our island. The difficulties are indefinitely 

 increased in comparing the formations of remote continents. But 

 these circumstances are compensated by the magnificent scale of de- 

 velopment of the successive groups, and their wide geographical 

 distribution. Taken together they have a great unity of character ; 

 and even in remote continents they seem to form a common base, 

 from which we may hope to compute the whole series of secondary 

 and tertiary deposits that surmount them. 



The author then briefly touches on questions of structure and 

 cleavage ; on the indefinite alternations of trappean beds ; on meta- 

 morphic structure ; on the long duration of the deposits ; and on their 

 great disruptions and symmetrical dislocations, indicating a greater 

 violence of disturbing forces than is indicated in the secondary for- 

 mations of this country. Following the geological scale of deposits 

 from top to bottom, we can trace a series of phsenomena indicating 

 the same kind of causation differing at different times in intensity 



