104 Association of American Geologists and Naturalists. 



Prof. H. added some remarks on the dip of the sandstone in general 

 in the valley, endeavoring to show that in part it was elevated by the 

 protrusion of the trap, and in part by the elevating and lateral move- 

 ments of the adjoining primary ranges, although it may have been de- 

 posited on a plane slightly inclined, but not on one so steep as 15° or 

 20°, which is the medium dip. 



Dr. Houghton remarked on the trap and sandstone on the 

 south shore of Lake Superior. 



Prof. Win. B. Rogers remarked upon some dynamical points 

 not considered by Prof. Hitchcock in his paper. 



Mr. Isaac Lea read a paper, " Observations on the Naiades." 



Mr. Lea in the introductory part of his paper, advocated the impor- 

 tance and beauty of the study of the natural sciences, and pointed out 

 the advantages of a minute knowledge of species in connection with ge- 

 ology. He then proceeded to state that the family of Naiades (fresh- 

 water muscles) was more variously diffused throughout the rivers and 

 lakes of the United States, than in any other country whatever. Atten- 

 tion had therefore been drawn to the development of this branch of 

 zoology much more successfully here than in Europe, where there were 

 not above a dozen real species, while the whole family consisted of 

 about five hundred accurately made out. He mentioned some of the 

 discoveries made here regarding their anatomy, habits, &c., and contend- 

 ed that the opposition made abroad to the large number of contested 

 species, must give way to the facts as most certainly established here. 



Mr. L. then went into a statement of the various parts of the Unto — 

 its soft and hard parts, (the animal and its calcareous covering,) and 

 dwelt more particularly on the secretions forming the shell, stated the 

 discoveries made recently in England by Dr. Carpenter, and particular- 

 ly of that very important one of the " basement membrane," (similar 

 to the reticulated epithelium in the mammalia,) by which the calcified 

 portion of the shell is formed. The apparatus of the hinge and ligament 

 was also minutely described, and the position of the shell in its native 

 element shown, together with the normal characters of the parts, pre- 

 cisely and definitely fixing in description its anterior and posterior mar- 

 gins, &c. He then went into the divisions and subdivisions of the Nai- 

 ades, in accordance with the system proposed by him in his synopsis, 

 and illustrated his remarks by specimens of the types. In describing 

 the habits of the Unio, he stated that it was sometimes left by freshets 

 on the shelving shore, down which it travelled to its native element, leav- 

 ing a grooved track to mark its progress. Mr. L. then, turning to his 

 friend. Prof. Hitchcock, who has so happily illustrated the bird-tracks of 

 the new red sandstone of Connecticut, suggested to him that he should 



