J. E. Hyde — Desiccation Conglomerates. 405 



tunately nothing has been recorded to show how hard, such a 

 lime surface may become when exposed to the sun for some 

 time, but Professor Alexander Agassiz notes that on the 

 Florida coral islands the interval of time between two tides is 

 sufficient for the formation of a thin film of hard, ringing lime- 

 stone on the surface of fine coral sands.* 



The best example of a conglomerate formed by the breaking 

 up of a sun-cracked lime-mud surface was seen near Bellaire, 

 Belmont county, Ohio. The exact point is in a clay pit on the 

 south side of McMahon's creek about one and one-half miles 

 above the point where it empties into the Ohio river at Bellaire. 

 Here an argillaceous shale lying above the Pittsburg ^ coal is 

 mixed with a sandj' shale lying below it and used for making 

 brick, but the combination contains so much lime that constant 

 care is necessary to insure success. Following is the section 

 exposed in the pit from above downward : 



9. Limestone in several beds with thin shales be- 

 tween, some of the beds one foot thick 8 f t. + 



8. Gray argillaceous shales with many limestone 



nodules , . 5 to 5 1/2 ft. 



1. Dark gray and black shales 1 ft. 8 in. 



6. Roof coal of Pittsburg seam 2 ft. 10 in. 



5. Soft gray argillaceous shale 2 in . to 1 ft. 2 in. 



4. Coal, Pittsburg seam 5 ft. 1 in. 



3. Dark gray argillaceous shales with considerable 



carbonaceous matter 2 ft. 4 in. 



2. Gray amorphous limestone, bottom very irreg- 



ular and thickness abruptly variable as a 

 result of the uneven surface on which it rests ; 

 top horizontal and unaffected by the irregular 

 lower contact. At the top of this bed occurs 

 the conglomerate to be especially described, 1 ft. to 1 1/2 ft. 

 . Sandy micaceous shales, inclined at a sharp angle 

 to the overlying bed and separated from it by 

 an erosion plane. Such local unconformities 

 occasionally occur in the Coal-measures and 

 are not yet understood about 15 ft. 



In getting out the sandy shales for brick-making, the large 

 blocks of overlying limestone, number 2 of the section, are 

 thrown aside and after short exposure all the dark shale adher- 

 ing to the upper surface weathers off, exposing the conglomer- 

 ate layer in excellent shape. The conglomeritic portion is only 

 one half to one inch in thickness and is preserved on the sur- 

 face of these blocks exactly as it existed at the time it was 

 covered by the shale. Throughout the entire opening, cover- 

 ing perhaps three or four acres, it maintains its character and 

 * " Three Cruises of the Blake," vol. i, p. 87. 



