LANE ON RECENT WORK OF THE GEOLOGICAL SURVEY. 39 



one degree in G8 feet. We oujilit to have a few more observations 

 because variation of the tlierinal giadient of Mioliigan is a matter of 

 more than local interest. The deepest mines of the world are in this 

 State and in them the gradient is 1 degree in not less than 107 feet 

 I hope to be able to get a few more thermometric observations. 



The workers of the Upper Peninsula are still engaged in the correla- 

 tion of the copi)er bearing lodes and the acquisition for science of the 

 abundant data ottered by the new explorations. This is of practical 

 as well as scientific value, while Dr. Hubbard tells me that in one case 

 of which he knows, in estimating the value of land as containing the 

 P.altic lode, the supervisors were more than a mile ott". 



Our Railroad Commissioner, iCr. Chase S. Osborn, has invited me to 

 visit with him some large caves in the Niagara limestone of the Upper 

 Peninsula, and I should be glad to have all who are interested in cave 

 life, visit the place. 



The work just now in hand in the Lower Peninsula is largely con- 

 cerned in the study of marl and the correlation of the various coal 

 seams. The new exi)lorations for coal are bringing to light a fauna 

 and flora little by little, which has been sent to Washington for identi- 

 fication, and shows an equivalence with the Pottsville formation, i. e., 

 what was formerlv known as the Millstone Grit. 



