Handbook of Paleontology 225 



except at the top of the series. Occurrences have been 

 found as far south as eastern Massachusetts (Brain- 

 tree). Middle Cambrian beds have also been found in 

 eastern New York (p. 237) and in northern Vermont. 

 The Middle Cambrian beds of the Cordilleran trough 

 belong to the Pacific Province and carry an entirely- 

 distinct fauna from those of the Atlantic. Here are 

 found the best Middle Cambrian sections and only here 

 are there transition faunas between Middle and Upper 

 Cambrian. Elsewhere the absence of transition faunas 

 indicates a break in deposition (eastern America). At 

 Alberta, Canada, 8300 feet of deposits have been meas- 

 ured, mostly limestone, but including some beds of 

 shale such as the seven-foot thick Burgess shale which 

 through the labors of the late Doctor Walcott has fur- 

 nished a remarkable fauna of crustaceans, worms, holo- 

 thurians (sea cucumbers) etc. which have not been 

 seen elsewhere. The sea continued to transgress 

 through the Middle Cambrian, and through Utah, 

 Montana and elsewhere in the northwest the first 

 Cambrian beds of marine nature belong to the middle 

 epoch. The Upper Cambrian is also known as the 

 Si Croixian epoch from its occurrence in the St Croix 

 river region of Wisconsin. This series of beds will be 

 found in many earlier works classified as early Upper 

 Cambrian with the beds of the lowest series of the 

 Ozarkian system representing the final series or upper- 

 most Cambrian. The St Croixian of the upper Missis- 

 sippi valley includes the youngest true Cambrian 

 known, that is, the Cambrian as developed in America 

 by Walcott and Ulrich. The three upper formations 

 there are rarely or not at all represented in the Appa- 

 lachian valley. The seas spreading eastward from the 



