292 PKOCEEDINGS OF THE GEOLOGICAL SOCIETY. 



and their contents, coming from the S.W. He calls it therefore a 

 '^ colony," adventitious and owing its existence to the argillaceous 

 nature of a few deposits and the presence of a little lime. We have 

 to remark that it is a colony without an ascertained source, without 

 a mother- country, so far. No such phenomenon is known else- 

 where. M. Barrande acknowledges that he knows of none. There 

 is no instance in ISTew York or Wales, as far as I am aware, of a 

 single thin fossiliferous band, being developed after a long interval 

 of time into a great stage. Species and genera, individually, may 

 and do recur, but organic groups never — they are seen but once. 

 There are mineral intrusions, or intercalations, such as Tully Lime- 

 stone in the Hamilton Rocks of New York ; but its fauna is not all 

 peculiar, and it does not recur. 



§ 9. Comparison of the PalceozoiG Basins of Wales and New York. 

 — Leaving these subjects, we may be allowed to state that the pro- 

 priety of having studied the order in which fossils were introduced 

 into their respective beds, their increment and decrement, and other 

 topics which have engaged our attention, will be well seen in com- 

 paring the basin of New York with that of Wales. But, as I shall 

 perhaps be able to lay before the Society such a comparison in a more 

 detailed form, I here only present a simimary of the more character- 

 istic points. I premise these statements by the observation that 

 both these geological areas appear to have been constructed on the 

 same great comprehensive principles, and nearly of the same mate- 

 rials, — two most important considerations. One very great distinc- 

 tion between them, however, is, that they have received different 

 dynamic treatment, in the frequency of plutonic disturbance in Wales 

 and its comparative absence ia New York, — such dynamic treatment 

 involving, it must be kept in miad, both gradual and sudden changes 

 of population. While the strata of these areas are formed of much 

 the same mineral substances, the conditions of these, their order and 

 quantities, are very varied. For certain leading particulars, the 

 former portion of this Part III. may be consulted. 



The points of Zoological Similarity may be summed up under the 

 following heads or laws : — 1. The organic remains of both basins 

 belong to the same orders and genera, unmixed with those of other 

 sedimentary systems, as Permian, Jurassic, &c. 2. Vertebrate 

 animals were introduced at nearly the same date. 3. The organic 

 remains approximate closely in general facies. 4. They ajQfect strata 

 of the same mineral character in both, — the majority preferring the 

 calcareous, the others the arenaceous form of deposit. 5. The 

 great majority exhibit the same order in their introduction and dis- 

 tribution. This is seen in Orthis, Pentamerus, Spirifer, and other 

 Brachiopoda ', and in Endoceras, Qraptolites, Trilohites, Sfc, the 

 more highly organized being often prominent in the early stages. 

 6. The law of divergency into several matrices is the same, or 

 nearly so, in the two basins, the number of instances being fewer 

 in New York. 7. The great majority of animals typical or recur- 

 rent in one basin are so in the other. 8. The great majority of 

 the recurrent fossils in both occupy the same nimiber of epochs. 



