36 THE CANADIAN NATURALIST [Vol. vii. 



which have to such an extent obliterated all access of approach 

 that their study can oaly be of the most partial nature. It is 

 only along some of our river channels, and at intervals on the 

 margin of the lake, that there is sufficient room for either strati- 

 graphic or palaeontological investigations. The fundamental 

 rocks of this district belong, with but one or two exceptions, to 

 Ihe Corniferous limestone formation of the Middle Devonian 

 system. These Devonian rocks of America, as laid down by the 

 New York geologists, consist of the following grand sub-divisions 

 or Periods, viz. : 1. The Oriskany sandstones, 2. Corniferous 

 limestones, 3. Hamilton shales and sandstones, 4. Portage and 

 Chemung groups, and 5. The Catskill red sandstones. The 

 following may be given as a table shewing approximately the 

 geological position of the different formations observed either as 

 outcrops or by borings in the area in question : — 



{ Corniferous limestone formation. 

 Onondaga limestone. 

 Schoharie grit. 



. T-> • f Cauda-galli grit. 



Lower Devonian. < r\ ■ i ^ ^ 



\ Oriskany sandstone. 



/ Lower Helderberg group of Vanuxem, including 



-^T ,,., . \ the Tentaculite limestone, or so-called Water- 



Upper bilurian, J ,. i ^- • • 



^^ ^ lime sub-division. 



( Onondaga formation, or Salina group of Dana. 



[■ Guelph and Gait limestones. 

 ,,. ,,,,,.,• ! Niagara formation. ^ 



Middle bilunan. j ^^.^^^^ , f ^^.ticosti group. 



[ Medina " J 



Of the subdivisions of the Middle Devonian System only one is 

 found in the locality under consideration. This is the Cornifer- 

 ous limestone formation, which forms by far the greater portion 

 of the underlying surface rock. The Ijower Devonian is not 

 apparently represented in this County, although numerous frag- 

 ments of the Oriskany sandstone are scattered here and there on 

 the surface of the ground as angular and evidently lately detached 

 erratics. The rocks of the Lower Helderberg group of the 

 Upper Silurian series are, with the exception of the Tentaculite 

 limestone or Water-lime beds, entirely wanting in Ontario. This 

 division is described by Vanuxum as being essentially a dark 

 blue magnesian limestone, with interstratified drab-colored beds 

 which yield by calcination a very valuable hydraulic cement. It 

 is met with in two localities in the County, and in each presents 

 similar lithological characters. The Onondaga Salt group, or 

 Salina formation of Dana, is found to extend under the whole 



