REPORT OF THE DIRECTOR 1916 153 



graptolites. Nobody as yet knows die total thickness of the Trenton 

 beds in the Champlain valley, but the exposures are very numerous 

 and easy of access. A short row from Cliff Haven brings one to 

 Crab island, and by automobile Cumberland head or Long - point 

 are quickly reached. These are all excellent localities for studying 

 Trenton beds and for collecting from them. There is a fascination 

 in the study of these ancient stamps or seals, but we shall not really 

 appreciate their significance until we become familiar with at least 

 some of the lessons they can teach. It is of importance that we 

 notice one of these now. 



Bulletin 92 of the United States National Museum is entitled 

 " Bibliographic Index of American Ordovician and Silurian Fos- 

 sils." It is a work of 1521 pages. On pages 1448 to 1452 a list 

 is given of 524 different species of fossils found in and described 

 from American beds of Chazy age. Following this is a list of 

 1080 different species found in the deposits of Trenton age. On 

 comparing these long lists the student will be surprised to find that 

 only 8 species are common to both groups of rocks. Some of the 

 fossils in these lists are known to range through all the various beds 

 of a single formation but there are others that are restricted to a 

 single " zone " or to a series of thin sheets of deposit which 

 together measure but a few feet in thickness. Knowing the short 

 ranging species and their mutations one can identify the particular 

 zone of any formation now exposed at the surface ; and knowing 

 how thick the formations are in any given locality, a geologist is 

 able to tell the seeker for mineral wealth just what formations he 

 would go through and the approximate thickness of each, if he 

 should sink a shaft in any thoroughly studied locality. For instance, 

 a boring made in the immediate vicinity of the Boston Cottage 

 would pass through postglacial deposits and then enter the boulder 

 clay of the glacial period. About 30 feet below the surface the 

 Trenton rock would be encountered. As the local thickness of 

 this formation is not yet known and as the particular zone exposed 

 here has not yet been determined, it would not be possible to give 

 the actual depth at which the Black River formation would be 

 reached. The Black River limestone would, however, be the 

 next formation encountered below and would have a thickness of 

 less than 10 feet. Under this about 20 feet of Lowville rocks would 

 be encountered and under these the Chazy would be found. The 

 thickness of the latter formation would here be about 900 feet. 

 After passing through the Chazy beds we would enter those of 

 Beekmantown age and the sequence is known to still greater depths 



