NICKLESANDBASM.KR.] OEOrTRAPHIC BISTRIHUTION. 63 



the Baltic- S(MU Engliind. and Scotland, contain most of the Paleozoic 

 sti'ata which have thus fai- yielded l)ryozoa. Three or four times as 

 many species have been made known from North America as from all 

 the rest of the world. 



The ear'i&5t, bryozoa, so far as we now know, are in the Chazy. 

 Thev are low in numl)ers, but this mav be because they have not been 

 systematically collected and studied. 



The Trenton period, in all its subdivisions. Stones Riven- (Birdseye), 

 Black River, and Trenton proper (including the Galena), is a vast tomb 

 of bryozoa. The seas seem to have swarmed with these minute crea- 

 tures. In eastern Canada and New York, thence stretching through 

 Ontario to the northwest into Wisconsin. Minnesota, and Manitoba, 

 are deposits following roughly the outline of the northern or north- 

 eastern border of the interior sea. Deposits formed along what was 

 soon to appear as an island or islands — the Cincinnati anticline — are 

 also open to our inspection in Kentucky and Tennessee. At isolated 

 points in Illinois and Missouri Trenton deposits are also exposed. 

 Also isolated tracts of early Silurian times are exposed in the western 

 highland. The Trenton is preeminently a continental formation. 

 Scarcely anywhere between the two highlands does the drill fail to 

 show Trenton if sent deep enough. 



The succeeding period, the Cincinnati — by some authors still termed 

 the Hudson River group, though the name seems to be a misnomer — 

 is again a formation of continental extent, in which bryozoa flourished. 

 The deposits in eastern New York along the Hudson River, supposedly 

 of this age, have yielded no bryozoa and few other fossils. The Utica 

 shale and the Lorraine and Pulaski shales and sandstones in the region 

 of the Mohawk Vallej^ and southeast of Lake Ontario were formed 

 under conditions not generally propitious for bryozoa. But in the 

 interior, in the region of the Cincinnati anticline, conditions were con- 

 genial and bryozoa flourished. Ohio, Kentucky, Indiana, and some 

 limited areas in Illinois, Minnesota, AVisconsin, and Iowa, all yield 

 well-preserved br3"ozoa and usually in great abundance. Outcrops 

 occur also in Canada and as far east as Anticosti Island, in the gulf of 

 St. Lawrence. 



The Upper Silurian deposits in this country' are exposed rather 

 locally. Many of them were formed under conditions Avhich precluded 

 bryozoan life, but in some bryozoa are exceedingly abundant. From 

 the Medina and Waterlime no bryozoa have been made known. The 

 Clinton has jaelded a considtM'able number both in New York and in 

 Ontario, as well as around the l^ordors of the Cincinnati anticline, but 

 they are seldom tinely preserved. The Niagara deposits are generally 

 of a character unfa\'orable to the preservation of its fauna, but there 

 are two good exceptions — an area in western New York, typically 

 exposed at Lockport, and one in the vicinity of Waldron, Indiana. 



