134 Geological Equivalents. 
since.* Here is a case, therefore, where strata may be examined in 
place throughout a great extent of country ; but intrinsic characters 
are still required for determining their true position as a general mass, 
compared with European strata or with those of other districts in 
America. 
From a consideration of the cases here referred to, intrinsic char- 
acters, more definite than any left us by Werner, seem to be essen- 
tial to the progress of the science. The enumeration of mineral con- 
stituents of rocks, can never be satisfactorily applied. Unorganized 
matter presents but few characteristics. Naturalists find it a more 
difficult task to describe, by external characters, about two hundred 
and seventy species of minerals, than fifty thousand species of plants, 
and a still larger number of animals. 
It isa subject of high congratulation to students in geology, of our 
day, that the illustrious Cuvier, aided by the Brongniarts and their 
coadjutors, have extended the science of organic nature to the science 
of geology. We are no longer limited to the enumeration of mineral 
constituents. We find the same organized remains associated with 
equivalent strata, in every part of the earth; though they often ex 
tend into several adjoining strata, which are probably cotemporaneous, 
or nearly so. Were every species of organized remains examined, 
described, and figured ; geologists could correspond as understand- 
ingly, as botanists can now correspond on the subject of plants. Great 
progress has been made in the science of animal relics; and the wor 
of Sowerby, Goldfuss, and others, already begin to place students 
geology on the real course towards the truth. M. Adolph. Brongniatt 
will soon relieve them from all embarrassment among vegetable fossils. 
As no attempt has hitherto been made for shewing the relation 
ship between European and American strata, by a general enumeli- 
tion of the organized remains in American strata, I offer the following 
imperfect list, as an attempt towards the establishment of the most 
important starting points. 1 confine myself to those strata, which are 
acknowledged by the geologists of both continents—leaving out all 
* The map referred to was prepared for this Journal, at the expense and direction 
of Gen. Stephen Van Rensselaer; and will appear in it as soon as I can prepare 
n explanations. It has been inserted at the end of a small text-book, i * 
few copies only. 
he best specimens found in the shelly variety of carboniferous (metallifero™) 
lime-rock, and in the second graywacke, (coal grit,) did not arrive in seaso? for ths 
article. Our boxes were detained by a breach in a canal, and other con 
I hope soon to be able to add them, and the specific names of our vegeta 
collected chiefly in Pennsylvania. 
tingencie® 
ble fossi® 
