STRATIGRAPHIC TAXOKOMY 675 



tinent from the north Atlantic between Newfoundland and Labrador. 

 From here it extended southwest ward up the Saint Lawrence trough to 

 northern A^ermont, from where it passed in a more southerly direction 

 through this State into eastern New York, presumably joining the At- 

 lantic again in New Jersey. Through most of this extent the deposits 

 in this channel are buried beneath other sediments — slates, limestones, 

 and quartzites, perhaps chiefly of Cambrian age — ^which have been thrust 

 northwestwardly over them. Here and there the Levis shale is at the 

 surface, but whether this is because the belt was not entirely buried in 

 such places, or whether erosion of the overthrust sheet has again un- 

 covered it, remains to be shown. Besides, we do not yet know exactly 

 how to discriminate the four or five kinds of shale and slate in the 

 Taconic-Saint Lawrence slate belt, unless we are so fortunate as to find 

 characteristic fossils. But no determined and well equipped effort has 

 yet been made to ascertain the lithologic peculiarities of the several 

 beds. Although I have spent but little time in the slate belt, it was 

 sufficient to convince me that serviceable differences in character, asso- 

 ciation, and sequence of rock types can be worked out. The "slate belt'^ 

 contains lower Cambrian shales and two Canadian shales, one of them 

 the Levis shale, the other a crumpled and more or less metamorphosed 

 shale that has been pushed westward over various formations, and which 

 seems to constitute the greater part of the "Taconic slates." Besides 

 these the western part at least contains Ordovician shales — the Norman- 

 skill and perhaps other distinguishable beds. These four shale zones, I 

 believe, can be discriminated and mapped separately without extraor- 

 dinary difficulty. 



The most southerly outcrop of Levis shale so far discovered is the 

 one on Deepkill, in Eensselaer County, New York, which has been fully 

 described by Ruedemann. He found here an excellent representation of 

 the graptolite faunas long ago collected by the Canadian geologists in 

 the vicinity of Quebec and somewhat later in Newfoundland. That the 

 beds exposed at these three points were laid down in a long channel that 

 communicated at each end with the Atlantic, and may, therefore, have 

 been a current-swept thoroughfare, is inferred from the universally 

 accepted belief concerning the pelagic existence of the graptolites. Being 

 unquestionably floating organisms, therefore dependent on currents for 

 their dispersal, it seems an utter impossibility for them to have floated 

 a thousand miles \i]) a narrow bay, which, so far as T can see, is the only 

 alternative explanation of these longitudinally distributed beds. (See 

 page .*iTl : also paper by TJiiodomami in the Juno issno of this: vohiino.) 



