330 



BLACK, BITUMINOUS, ALUMINOUS SLATE. 



Underlying the sandstones above noticed, though also nowhere ob- 

 Berved to make an outcrop within the portion of the State now under 

 consideration, there is a well characterized, black, bitumous slate. This 

 rocii makes an outcrop much farther to the north, and is described by 

 Mr. Douglass, in his accompanying report, to Avhich I refer you. This 

 slate conbiins much sulphuret of iron; it will burn readily, and in gen- 

 eral character an I position, it agrees with the bkck shale stratum 

 of Ohio and Indiana, but its thickness is probably not nearly so 

 great 



LIMESTONES OF LAKE ERIE. 



Thi.i formation, which immediately underlies the black slate, is by far 

 the most continuous and extensive rock formation in the western States. 

 It is found outcroping in seveial district ranges throughout Monroe 

 County ; forms a considerable part of the lake coast, and serves as a ba- 

 sis to the islands at the mouth of the Detroit River, and is an exten- 

 sion of the rock formation, which occupies the whole western part of 

 Ohio, and the northern and eastern portions of Indiana. It is found 

 forming the bed of Lake Michigan at its head, and undoubtedly is the 

 underlying rock of a considerable portion of the extreme south-western 

 part of our State. The overlying tertiary clays, conceal a great part of 

 this formation. , 



The character and economical adaptation of these limestones hav« 

 been sufficiently set forth in former reports, to which, accordingly, I re- 

 fer you for detailed information. 



Amonsr the fossils contained in the limerock, I distinsfuish the follow- 

 ing genera: 



Calymene and Asaphus, Cyathophyllum, Productus, Terebratula, 

 Spirifer and Dethlyrus, Bellerophon, Atrypa, Strophomena, Orthocera, 

 Encrinup, Retepora and Madrepora. 



In proceeding southeily from the outcrops of the slates of Lake Hu- 

 ron, a liuicrock is met with, which may be seen in the bed of a small 

 stream n<'ar the lake coast, town nine north, sixteen east. In character 

 and fossil contents it beam a resemblance to that of Monguagon, Mon- 

 roe county, but its position would seem to indicate it rather as an inclu- 

 ded stratum in the series of sandrocks and shale, which are higher in 

 the geological series. 



