192 MICHIGAN ACADEMY OF SCIENCE. 



of the paleontology of the belts, but did not materially change their 

 distribution or subdivision, in fact, he was less inclined to minute divis- 

 ion than Winchell. In Vol. Ill he transferred his studies to the Lower 

 Peninsula, and this volume is a treasure house of observations upon the 

 rock geology of the Lower Peninsula. One has to be thorough to find 

 any rock exposures which he did not visit. He made also extensive col- 

 lections of fossils, and the second part of the volume contains elaborately 

 illustrated paper on corals. Dr. Rominger gives us not a few records 

 of deep wells, and an appendix contributed by Dr. Garrigues calls atten- 

 tion to the different chemical character of the brines.'' They also begin 

 to appreciate how much thicker the geological column is than Winchell 

 had been able to estimate from surface observations. Dr. Chas. R. 

 Wright succeeded Dr. Rominger and when he died, leaving matters 

 unfinished, I had to take up and prepare for publication the records 

 which he had gathered during the great drilling excitement of 1885-7. 

 This added a bundle of new facts which were incorporated in Part II of 

 Vol, V, and my papers on the Water Supply of this State. 



Little by little the drill, going down now for salt, now for oil or gas, 

 now for water for the farm or city, or for mineral water, has added to 

 our knowledge of the geology of the Lower Peninsula and enabled us to 

 improve a little up(m the boundaries laid out by the first geologists, 

 jet in the main their work has stood the test of time. The main factor 

 which is coming put is that there are minor flexures in the general basin 

 like structure which was correctly found by the earlier Surveys. This 

 shows in some of the cross sections given in my Coal Report. In regard 

 to the salt, the following difl'erent brines may now be distinctly 

 recognized : 



1. The brine of the Parma Sandstone and the Grand Rapids 



Group, which is high in sulphates. 



2. The brine of the Marshall Group, which is relatively free from 



sulphates but contains the earthy chlorides and valuable 

 amounts of bromine. 



3. The brine of the Berea Grit. This was perhaps first identi- 



fied as such by Rominger in the old Ann Arbor wel], but is 

 also the source of the Huron County brines. 



4. Brines of the Traverse and Dundee, the Devonian Limestones. 



Gas and oil are liable to be associated with these and par- 

 ticularly H, S. 



5. Beneath this comes the rock salt from which a brine is de- 



rived by letting down water from the surface. 

 There are of course other brines in Niagara and Trenton, but these are 

 those of most commercial importance. 



Much exploration has been carried on for oil and gas, but it has been 

 very largely on the strength of surface deposits or signs and the results 

 have been disappointing except near Port Huron. We have, however, 

 beyond question the oil and gas bearing rocks, and it is only a matter 

 of time when reservoirs of these substances in commercial quantities 

 will be found. 



Wliile coal has long been known, it is only recently there has been 

 much developed, and that material for correlation from other regions 



