MUSEUM OF COMPARATIVE ZOOLOGY. 23 



hundreds of feet, belonging to the Paradoxides section of the Cambrian, 

 exists on the southern shore of Massachusetts Bay in the township of 

 Braintree. This deposit probably extends, as a continuous mass or as 

 an isolated section, as far as the Neponset River in Quincy, a distance 

 of about four miles. Although no distinct fossils have been found, save 

 at Braintree, a number of distinct remains occur near the Neponset 

 River, in beds having much the same aspect, and apparently at about 

 the same distance from the syenites, as those at Braintree. It there- 

 fore, on account of the large extent of the Paradoxides section about 

 Massachusetts Bay, seems possible that the Braintree section may be 

 represented somewhere iu the Attleborough Cambrian district. 



Although I spent a good deal of time searching for rocks which should 

 have a physical likeness with those at Braintree, I have not yet been able 

 to discover any such in the Narragansett field. The conditions under 

 which the search was made render it difficult to make sure that such 

 deposits may not yet be found in that vicinity. A search for the Attle- 

 borough series in the Boston synclinal and in the neighborhood of the 

 Braintree beds has likewise been unavailing. No deposits of conglom- 

 erates or saudstones having the peculiar hue of that series have been 

 found in any part of the Boston basin. I therefore regretfully conclude 

 that the probability of determining the relative position of these two sec- 

 tions in this field is small. The absence of one of these members of the 

 Cambrian series from the Boston basin and from that of Attleborough 

 may be fairly attributed to the large amount of erosion to which both 

 regions have been subjected. The Paradoxides beds of Massachusetts 

 Bay are evidently a mere remnant of a sheet which once overspread a 

 large part of that area. The extensive conglomerates belonging to the 

 Roxbury series, with their associated slates and the argillaceous deposits 

 of Cambridge and Somerville, are probably of Cambrian age, and may 

 possibly belong to the lower portion of that section, along with the Para- 

 doxides bearing strata. But it is barely possible that they may repre- 

 sent the same age as the conglomerates and shales which lie above the 

 level of the Attleborough fossiliferous horizon. The wide difference in 

 the mineralogical character especially of the slates makes this view, how- 

 ever, improbable. 



Although the relation of these two horizons is not determinable by a 

 comparison of the Massachusetts Bay and Narragansett deposits, it is 

 possible that it may be elsewhere determined. Fragments of sections 

 containing these horizons may well be foimd along other portions of our 

 Atlantic coast. 



