w. b. DWiaiiT. 145 



folds, the relative positions of which are complicated by 

 frequent "faults," while in some places several alterna- 

 tions of the Trenton and calciferous occur within the dis- 

 tance of a few feet. These phenomena occur both at 

 Rochdale and at Cliffdale, (the estate of Mrs. Andrew 

 Boardman), near the barns at the northeast corner of 

 the premises. The estimated width of a single thick- 

 ness of the Trenton, at Rochdale, is apparently from 

 seventy-five to one hundred feet, while that of the cal- 

 ciferous is estimated to be nearly three times as great. 

 There are probably four main folds of the two combined 

 limestones at the latter place. The narrow alternations 

 above mentioned require some special explanation, and 

 their cause is not to be hastily assumed. I have 

 thought them to be local slips, or ''faults" parallel 

 with the "strike." But to others they are strongly sug- 

 gestive of possible synchronism of the life of the two 

 sets of fauna, in consequence of which, according to 

 varying conditions, -alternations of one or the other were 

 possible. 



If this latter theory should be the right one, then we 

 have in these phenomena of our vicinity facts of emi- 

 nent importance in stratigraphical and paleontological. 

 philosophy. The more recent and careful investigations 

 which I have made, however, seem to me to favor the 

 former and more commonplace explanation rather than 

 the latter. 



There is another feature of much stratigraphic impor- 

 tance revealed by the later explorations. There is to-day 

 no apparent reason for receding from the ground pre- 

 viously taken, that the limestone identified as Trenton 

 and that called provisionally calciferous are entirely and 

 plainly distinct in their fossil fauna, and, as a general 

 rule, in their lithological characters. This is so pal- 

 pable that experienced geologists who have visited this 

 field have immediately yielded their assent to this fact. 



97 



