10 Twenty-fifth Refori on tee State Museum, 



as is practicable without the aid of better maps, the limits of the 

 Catskill group. My own observations lead me to believe that this 

 formation, so widely expanded in Pennsylvania, will be found to 

 enter the eastern part of the State of ITew York in the form ot 

 three low synclinals, the largest one of these forming the Catskill 

 mountain proper, with the lower and narrower ones lying to the 

 westward, constituting a portion of the same range. This position of 

 the formation is the one indicated by me in the Introduction to Yol. 

 Ill, Palseontology of ISTew York. The eroded anticlinals which 

 expose the Chemung group, have been those parts of the country 

 usually examined in the Catskill mountain region ; and with this 

 structure understood, it is easy to see how an observer may travel 

 upon the Chemung rocks from the northern part of Delaware county 

 to the southern line of the State, or even for considerable distance 

 into Pennsylvania, without becoming aware of the existence of the 

 higher formation. 



I hope by the end of another year to be able to communicate, in 

 a more definite form, our knowledge of the limite of the geological 

 formations in the south-eastern counties of the State. 



The collections of Mr. Herbert H. Smith have been made both for 

 the object of adding to our Lamellibranchiata from the Hamilton 

 group, and for tracing the range of species in a vertical and horizon- 

 tal direction. 



There is also another object to be finally attained by such collec- 

 tions, which I may indicate in this place. 



The greater part of these fossils, during their existence, were 

 essentially littoral in their habits, but in this respect certain genera 

 and species vary in their conditions of life. We find some beds 

 or zones of strata charged with great numbers of a few species, 

 while a succeeding bed, consisting of harder or softer material, may 

 be filled with species and genera for the most part quite distinct 

 from those below or above. Another fact is also to be noticed. 

 With certain of these lamellibranchiate forms there are Brachiopods, 

 while with others there are none, or rarely a few individuals. More- 

 over, as we go westward, we find the Lamellibranchiata disappear- 

 ing, and the Brachiopoda largely prevailing; while the strata, before 

 consisting of alternating beds of hard and soft material, have become 

 more homogeneous, and consist mainly of soft, calcareous shales. 



Now, these alternations of hard and soft beds, or beds of coarse 

 and fine materials, indicate more than the simple term expresses. 



