CONTRIBUTIONS TO PALAEONTOLOGY. 93 



In following tbeg>e strata in a southwesterly direction, the num- 

 ber of Brachiopoda has largely increased over those known in 

 New-York, and other fossils, unknown in New-York, have rp- 

 peared ; while some of the fossils most abundant here have ceased 

 altogether, or become rare in those distant localities. In Michigan, 

 on the contrary, the fauna above the Hamilton group, though 

 consisting almost entirely of species distinct from those in New- 

 York, has, so far as I know it, a more littoral character than that 

 of Southern Ohio, Indiana, Illinois or Iowa. Some portion of the 

 Michigan formations, between the Hamilton group and the Car- 

 boniferous limestone, should furnish us with land-plants for com- 

 parison with those of the Devonian rocks farther east ; since we 

 know that the Portage group, in its lower members, is well marked 

 in that region. 



Many years since, some of these Devonian plants were published 

 in the New-York Geological Reports, and, at a later period, in 

 the Geological Report of Pennsylvania : the investigations in the 

 Geological Survey of Canada have brought to light other species ; 

 and, still more recently, Maine and New-Brunswick have contri- 

 buted to swell the list. 



In tracing the course of the sediments, I have heretofore directed 

 attention to the evidences of the northeastern sources of the 

 materials ;* the probable greater extent of dry land in that di- 

 rection during the period of the Hamilton, Portage and Chemung 

 groups ; and consequently the probable greater development of 

 the Flora in that part of the country. This was inferred from the 

 fact that the larger proportion of the species found in New- York 

 were fragmentary, and apparently drifted specimens. 



In the study of the higher New- York groups, I have found, 

 accompanied by a gradual change in the sediments and in the 

 fauna, a gradual diminution in the number of species and of indi- 

 viduals of land-plants, as the investigations extended in a westerly 

 and southwesterly direction, until, on the southwestern confines of 

 the State, almost no specimens have been obtained. In the eastern 

 portions of the State, the upper beds of the Hamilton group are 

 everywhere charged with remains of land-plants ; but in the 

 western part of the State, their occurrence in this group is ex- 

 tremely rare. It is true that the species marking the Marcellus 

 shale continue, in a deposit of uniform character, as far as Lake 



* See Introduction to Vol. iii, Palaeontology of New-York. 



