524 
GEOLOGY OF THE FOURTH DISTRICT. 
With this condition of things terminated the Helderberg series of limestone, the last of the 
important calcareous formations in New-York. The ocean bed again subsided, and a deposit 
of dark mud was gradually precipitated upon it, while few organisms existed. Gradually 
vitality increased ; the dark carbonaceous mud became intermingled with calcareous matter ; 
living forms were multiplied, and, if possible, became still more numerous than in any 
preceding era ; the sea emphatically teemed with life, and the individuals of many species 
can only be enumerated by myriads. Soon, however, sand became intermingled with the fine 
materials ; a gradual change in the organisms supervened, and finally the sand predominated ; 
and throughout a long period, the accumulation consists of alternate deposits of argillaceous 
and arenaceous matter, or an intermixture of both, the whole abounding in organic forms. 
During this period were accumulated all the materials forming the Marcellus shale, the 
Hamilton group, and the Portage and Chemung groups. At the termination of the latter, a 
greater change supervened ; and though the formations are not widely different, all the pre¬ 
viously existing organisms disappear. 
Look, however, at this time, to that great portion of this ancient ocean, now occupied by 
the States of Ohio, Michigan, Indiana, Kentucky and Illinois, and even far west beyond the 
Mississippi. From the period of the final deposition of the Helderberg limestone, to the com¬ 
mencement of the Carboniferous era, this vast expanse was comparatively a solitude. Instead 
of the busy multitude thronging every part of the sea farther east, this was cold, dark and 
deep ; presenting no beautiful corals, or the still more beautiful crinoideans, and with but few 
of the shells of the eastern waters, it more resembled a primeval ocean where vitality had but 
just assumed its place among the laws of nature. 
Beyond the termination of the New-York system, we might follow the successive formations 
through the Old Red Sandstone and Carboniferous periods, which exhibit the same changes 
throughout, as before described. In the latter system, we perceive the formation of an im¬ 
mense deposit of limestone at the west; while at the east, the ocean was accumulating only 
sand and clay. The same general law will be observed to exist in all the previous formations ; 
the proportion of calcareous matter constantly augmenting, and the arenaceous and argillaceous 
matter decreasing in a westerly direction. 
Such has been the mode of formation of the successive deposits, forming the subject of this 
Report; the operation of the same laws, and the influence of the same agents, as are now 
active, have produced this stupendous accumulation of materials. Subsequent operations have 
dislocated, elevated and overturned the indurated strata thus formed, and, together with the 
action of water, have produced the modern detritus, the soil of the surface, the fragments and 
transported boulders. 
The description of each rock has shown that the increment of fresh matter has almost 
uniformly been from an easterly direction, more especially of the purely mechanical deposits : 
this, according to a well known law of physics, must have first produced expansion in that 
direction, and consequently the eastern portion of our continent would first be elevated. 
