478 M. C. Lea — Nature of Certain Solutions 



the strata at the two latter localities were seen to be followed 

 upwards in a short distance by well characterized Eocene. 



Richly fossiliferous beds of the Upper Cretaceous lie along 

 the western slope of the Santa Ana Mountains, about one 

 hundred miles north of San Diego. The fauna is, however, 

 quite different from that of the localities just described, but 

 few species being common. Westward toward the ocean the 

 Cretaceous is followed by the Miocene without any apparent 

 physical break. Eocene fossils have not yet been found in this 

 region. Southward toward San Diego the Miocene is replaced 

 by the Eocene but the boundaries have not been made out. 



The Cretaceous bordering the Santa Ana Mountains dips 

 away at a high angle, and shows a basal conglomerate resting 

 unconformable 7 on the somewhat metOmorphosed Paleozoic 

 Series. 



The Lower Cretaceous has not yet been recognized in 

 southern California, unless it be in some local beds on the sum- 

 mit of the Carrizo Mts., on the western border of the Colorado 

 Desert. The locality is about seventy miles east of San Diego 

 and on the opposite side of the Peninsula Range. Fossils are 

 numerous but in poor condition, save for one species of the 

 coral Astrsea which is in large masses and exceedingly well 

 preserved. The beds are unconformable with the Miocene 

 and very much older. The region is a very interesting one 

 and deserves careful study. 



The discoveries announced in the foregoing article add 

 emphasis to the fact that too much care cannot be exercised 

 in classifying beds when only a scanty paleontological evidence 

 is available. The importance of stratigraphy and lithology 

 has been greatly undervalued in the study of California geology. 

 In my opinion it is one of the reasons that such serious mis- 

 takes have been made in the classification of the older rocks of 

 the Coast Ranges'. 



Art. LYII. — On the Nature of Certain Solutions and on a 

 New Means of investigating them ; by M. Carey Lea. 



[Read before the National Academy, April, 1893, by Dr. George P. Barker.] 



The three strong acids with which we are best acquainted 

 have this in common that they all form two classes of com- 

 pounds, the one perfectly neutral and perfectly stable in solu- 

 tion, the other class instantly decomposing when it is attempted 

 to dissolve them in water. As types of the first class may be 

 taken the alkaline salts. Of the second, mercuric sulphate, 



