118 Association of American Geologists and Naturalists. 



and these were proved to have influenced the development of organic 

 forms over the whole extent. During the earlier periods, a large pro- 

 portion of calcareous matter accumulated in the western waters, while 

 the purely mechanical deposits were largly developed at the east. As 

 a consequence of this condition certain forms were more perfectly de- 

 veloped at the west and southwest, while others were in greater abun- 

 dance and perfection in the eastern depositions. 



Since the period of the meeting in 1843, Mr. H. had had no opportu- 

 nity of investigating extensive tracts, but having had an opportunity of 

 examining and comparing a large collection made by Mr. Logan, in 

 eastern Canada, he presented the inferences drawn from these. In this 

 collection certain forms were found, which though common in the Lud- 

 low rocks of England, had not yet been detected in New York, nor so 

 far as known to him, in the United States. These were at the same 

 time, associated with other fossils, which occur in the Hamilton group 

 in New York ; thus offering a fact in proof of the correctness of the in- 

 ference of the New York geologists, that the Hamilton group was an 

 equivalent of the Ludlow rocks of Mr. Murchison. Similar facts were 

 shown to be true of several forms in the Hudson River group, in Cana- 

 da, which though not yet known in New York, were given in Mr. Mur- 

 chison's " Silurian System," as occurring in the Caradoc sandstone of 

 England and Wales. 



Another fact of interest was, that Capt. Portlock had figured many 

 organic remains, identical with those of the Hudson River group in 

 New York, but which Mr. Murchison had not given in his work. 



Other facts in regard to carboniferous species seemed to point to the 

 same inference ; and there seemed sufficient evidence for the conclu- 

 sion that certain forms disappear in either direction — or in other words, 

 that some species appear to be almost exclusively American, while oth- 

 ers are exclusively European ; that as we approach the eastern margin 

 of our continent, the forms are more allied to those of England, while 

 those discovered in Ireland, present us for the first time, on that side 

 of the ocean, with forms before known only in the United States. 



In connection with this paper, was presented a geological map of the 

 western and middle states. Upon this map were laid down all the prin- 

 cipal formations, showing their comparative development in the differ- 

 ent parts of the Union. This map was not presented as the result of 

 his own labors, but as the combined effort of others, who had very 

 willingly aided in the perfection of the map, by furnishing the materials 

 from their several regions. Among the gentlemen mentioned, were 

 Dr. Owen, Dr. Houghton, Dr. Locke, Messrs. Whittelsey, Briggs and 

 Foster of Ohio, Taylor and Ducatel, to whom and to others, full ac- 

 knowledgments are made in Mr. Hall's report on the geology of west- 

 ern New York, in which this map is published. 



