2® Human Foot-Prints in Solid Limestone. 



species of Pentremite here represented, (Fig. 3,)* is also a very 

 common fossil. Three other species have been ob- Fig^3. 

 served in this rock: the Peniremites ovalis of Gold., 

 the Pentremites florealis of Say, and the Pentremi- 

 tes globosa of Say.-f The above corallines and Cri- 

 noideans are peculiar to these beds. Hence I have 

 been accustomed to designate this group of rocks here 

 in the west, as the Pentremital limestone, and its up- Penti-rilliites 

 per bed as the Archimedes limestone. I am not aware pyriformis. 

 that these organic remains have been discovered in the Atlantic 

 states. It is upon the Archimedes limestone that our coal meas- 

 ures rest. Rising from beneath the great Illinois coal-field,;]: 

 these limestone beds circumscribe it nearly in its whole extent; 

 and wherever visible, one or other of the above characteristic 

 fossils can uniformly be found. These fossils afford a valuable 

 and trustworthy guide, in determining the limits of our true coal- 

 bearing rocks ; since no workable seam of coal has ever been 

 found, either in Indiana, Illinois, Kentucky, or Tennessee, be- 

 neath the rocks in which they occur. Without doubt some one 

 of these fossils can be discovered in the vicinity of St. Louis at 

 low water. I shall not fail to avail myself of the first favorable 

 opportunity of investigating this matter. 



* The Pentremites here represented, diifers a little from the drawing of the P. 

 pyriformis which I Jiave seen ; this specimen is much more angular or pointed 

 where the interscapuia joins the inferior extremity of the umbulacrum, and the 

 striag of the umbulacrum run slanting from above downwards, from the central fur- 

 row towards the interscapuia, instead of from below upwards. 



t A Pentremite, but of a species very different from any of these, occurs in a 

 stratum of rock at the falls of the Ohio ; the probable equivalent of the Wenlock 

 formation of Blurchison ; the same rock described in the reports of western geolo- 

 gists, and popularly known here as the cliff rock. 



X Delineated and described in my " Report of a Geological Exploration of part 

 of Iowa, Wisconsin, and Illinois, made under instructions of the Secretary of the 

 Treasury of the United States, in the autumn of the year 1839." 



I lake this opportunity of correcting an error with reference to tiiis same coal- 

 field, which has crept into a notice (in this Journal, Vol. xl, 1841) of a geological 

 survey of Indiana, which, as geologist of that state, I had made to its legislature 

 in the winter of 1838-9. In that notice (at p. 134) I am made to say: " Our bitu- 

 minous coal formation is part of a great coal-field which includes nearly the whole 

 of loioa, Illinois, and eight or ten counties in the northwest part of Kentucky." 

 It reads in my Report, " which includes nearly the whole of Loioer Illinois, and 

 eight or ten counties," &c. By a typographical error in the above notice which 

 converts the word Lower into Iowa, I am thus made to say, that this coal-field 

 extends over Iowa ; while, in point of fact, only a few townships in the southern 

 portion of that territory are included in the coal formation. 



