120 



but also those of Dr. Troost* and Dr. Locke, the state geologists 

 of Tennessee and Ohio. This memoir affords a general description 

 of a vast country lying between 35° and 43° north latitude and 81° 

 and 91° west longitude, including the States of Illinois, Indiana, 

 Ohio, Kentucky, and Tennessee ; throughout which enormous area, 

 the deposits are stated to belong chiefly to the Carboniferous and 

 Silurian systems. 



Of the exceptions to this distinction, consisting of strata of the 

 age of the Cretaceous system which overlap these palaeozoic rocks 

 on one frontier, and of other overlying deposits, to all of which the 

 author alludes, I need now take no notice. Adverting to certain 

 inferior masses beyond the Cumberland mountains which dip towards 

 the granite (the phsenomenon to which the Professors Rogers allude), 

 it is shown, that these dislocated bauds are surmounted by a series 

 of strata often containing abundance of organic remains. One 

 group of beds of shale, limestone and marl in the great Ohio valley, 

 and estimated to occupy a surface of 10,000 square miles, is re- 

 ferred, from its fossils, to the Lower Silurian rocks. The next 

 overlying mass consists, in great measure, of compact limestones, 

 which mineralogically might be mistaken for the Great Scar or 

 Mountain Limestone, but which the author now unhesitatingly 

 compares with the Wenlock formation, pointing out that it is co- 

 vered by other limestones and shales, and then again by a peculiar 

 sandstone, the whole of which represent the Lower, Middle, and 

 Upper Ludlow rocks. This vast series, characterized by Silurian 

 fossils, sinks under enormous troughs of strata which are referable 

 to the Carboniferous system, their base being composed of two bands 

 of limestone, one of which (containing Pentremites, and called the 

 Pentremital limestone) is compared with the Mountain Limestone 

 of England, though from the previous observations of Dr. Troost 

 this point may be doubtfulf . Can the lower limestone and part of 

 the supposed Upper Silurian represent the Devonian ? Lastly, re- 

 posing upon these, are two carbonaceous masses of prodigious ex- 

 tent, one of which, as lai'ge as Great Britain, is commonly known 

 as the great Illinois coal-field ; the other, occupying parts of six 

 states, covers an area of at least 50,000 square miles. 



In estimating the value of this memoir, I must express on the part 

 of this Society our obligations to Dr. Dale Owen, not only for his 

 lucid description of the order of succession in those great and im- 

 portant limestones, and for the clear sections by which they were 

 accompanied, but also for the very instructive suite of fossils cha- 

 racterizing each stratum, which he has presented to us. I have, on 

 a former occasion, alluded to the value of similar contributions upon 

 the older Rocks from the northern portion of the United States by 



* 111 his Sixth Geological Report to the General Assembly of Tennessee 

 (1841), Dr. Troost divides the Transition rocks of that state, and comparing 

 the fossils, he distinctly refers a large portion of them to the Silurian system, 

 saying that there are at least three or four divisions of that system in Ten- 

 nessee. 



t See Troost's Report, 1841, p. 21. 



