514 J- F. KEMP AND J. G. ROSS 



it has been found underground, and thus the best exposures and 

 the freshest rock have been obtained. Specimens were handed 

 to the senior writer in the fall of 1905 by J. G. Ross, the son of 

 Alexis H. Ross, and at the time Fellow in Mining in Columbia 

 University. The dike was announced and briefly described 

 before the Geological Society of America at the Ottawa meeting 

 December, 1905, and since then additional specimens have been 

 studied and an analysis has been prepared. The extent and 

 location of the dike have been worked out in detail by J. G. 

 Ross and his brother Donald. 



The dike is in the Masontown quadrangle and on the east bank 

 of the Monongahela River. It cuts across one of the small 

 tributaries of the Monongahela called Middle Run, at whose 

 mouth is the coal-mining town of Gates. To the southeast it 

 has been found as far as the little town of Edenborn, where, in 

 the coal mines of the Frick Coal Company, it pinches out, after 

 forming three separate branches. To the northwest, it appears 

 in the highway along the east bank of the Monongahela, but 

 efforts to find it on. the west bank have not been successful. 

 The details of situation are shown in Fig. 2. 



The local geology is shown in detailin the Masontown-Union- 

 town folio, No. 82, of the U. S. Geological Survey. The Monon- 

 gahela series is exposed along the river bank with the Pittsburg 

 seam, at the mouth of Middle Run, 240 ft. below the river. 

 The Monongahela series is 380 ft. thick at this point, so that 

 the Waynesburg seam is 140 ft. above the river. Still higher 

 the Dunkard series covers the hill-tops. The dike certainly 

 cuts the Waynesburg seam and rises at least 20 feet higher in 

 the overlying Dunkard series. 



On the surface the dike is narrow wherever discovered and is 

 single, except at the crossing of Middle Run. The observed 

 thicknesses vary from about one foot to about 3 feet, except in 

 the Waynesburg coal where it is 10 feet. Under ground, how- 

 ever, where the opportunities for exact study are better, the 

 thickness at the horizon of the Pittsburg seam reaches a reported 

 maximum of 35 feet. The dike moreover is known to split up. 

 At the southeast, as it runs out, there are three narrow branches, 

 each a few inches across. At the extreme northwest there are 



