402 



THE CAMBRIAN. 



(BULL. 81. 



development of fossils occurring at the same point, proves the organic forms to have 

 flourished in a littoral position; and beyond these points, where the thinning of the 

 strata indicates a greater distance from the shore the fossils diminish, and at the more 

 distant and deeper points are not found at all. There is no evidence of denudation 

 in these instances, and if there had been the parts left would have retained the same 

 fossils, had it ever contained them, as they do farther east. 



Throughout that part of the ancient ocean now occupied by Ohio, Indiana, Mich- 

 igan, Illinois, and even to the west of the Mississippi, there appears to have been 

 comparatively a small number of living forms existing from the period of the final 

 deposition of the Helderberg limestones to the commencement of the Carboniferous 

 period ; while in New York, during the same period, there were a greater number of 

 forms and individuals than in all the preceding periods. Without desiring to dimin- 

 ish the value of fossil characters as means of identifying strata, it must still be 

 acknowledged that similar conditions in the bed of the ocean, and apparently similar 

 depth of water, are required to give existence or continuation to a uriform fauna; 

 and when we pass beyond the points where these conditions existed in the ancient 

 ocean, we lose in the same degree the evidences of ideutity founded upon fossils. 

 Some species, it is true, have lived onward through successive depositions, often of 

 very different nature ; yet, at the same time, these may not have had a very wide 

 geographical range. In the case before us, some species have lived during the deposi- 

 tion of all the rocks from the Hamilton through the Chemung groups, and yet they 

 have never extended themselves as far westward as Ohio and Indiana, although the 

 nature of the deposits there was as favorable to their existence as in New York. 



For the distance of 100 or 200 miles from the shores of the present continents the 

 forms may be similar — we know not but they are — still who can say what changes may 

 occur, or whether any exist in the depths 1,000 miles from land ? From the nature of 

 sedimentary deposits it can be only the finer parts that ever reach to great distances 

 from their origin; and, reasoning thus, the fauna of the deep and distant parts of 

 the ocean, if any exist, would be uniform, not being liable to destruction or change 

 of condition from the rapid invasion of variable deposits like those near the shore. 

 The deposition of a coarse sandstone or conglomerate succeeding to a shaly mass would 

 in all probability destroy the greater number of living forms as far as it extended. 

 But at the same time, the finer materials produced by the same cause would extend 

 far beyond the limits of the coarser, and thus approximating in some degree to the 

 lower mass, the fossils might be continued long after they were destroyed at another 

 point. 



One of the most interesting changes in the products on going westward is the 

 great increase of carbonate of lime and the diminution of shaly and sandy matter, 

 indicating a deeper ocean or greater distance from land. The source of the calcareous 

 deposits is thus shown to have been in that direction, or in the southwest, while the 

 sands and clays had their origin in the east, southeast, and northeast, producing a 

 turbid condition in the waters of these parts during long intervals, which was un- 

 favorable to the production of calcareous matter and the formation of chemical 

 deposits. In New York we are evidently upon the margin of this primeval ocean, as 

 indicated in the character of the deposits as well as organic remains; the southwest 

 unfolds to us that portion where greater depth and more quiet condition prevailed. 



At a later date he said : 



I have met with no essay upon the geographical distribution of fossils in the older 

 rocks ; and the few facts here and there gleaned serve rather to stimulate than to sat- 

 isfy curiosity. It has been a favorite opinion of many, and frequently advanced, that 

 the condition of this ancient ocean was uniform and its depth moderate, and that 

 the uniformity of organic products affords proof of the same. Without pretending 

 to refute any theories or to establish general conclusions for the whole confluent or 

 for the whole globe, I shall merely offer a few facts which have fallen under my own 

 observation, and this with the hope of calling the attention of other observers to the 



