356 PROCEEDINGS OF THE GEOLOGICAL SOCIETY. [April 5, 



red mariy limestones of the upper Lias and Jura, or the fossil remains 

 which accompany them. The dark fossiliferous marls of the lower 

 Lias are here continued to the limits of the dolomite, which is seen 

 immediately resting upon them. 



§ Remarks upon the Diluvial and Erratic Phenomena. 



The diluvial and the alluvial deposits could not be indicated by 

 different colours on the map. Mere alluvial and detrital accumula- 

 tions in the higher parts of the mountains were not separately marked. 



It may be of some interest to advert to the two diluvial terraces 

 in the valleys of the Loisach and of the Tsar. They consist of hard 

 conglomerates, containing pebbles of the different sedimentary rocks 

 of the Alps, mixed with erratic pebbles, which go down to the very 

 lowest visible beds. The terraces attain a height of 120 and 180 

 feet above the level of the rivers. They show us the great thickness 

 of the diluvial beds with which the Alpine valleys had been covered 

 before the denudations by the present rivers took place. 



One of the most interesting phccnomena which occur ia the study 

 of the Alpine dilu\dum is offered by the erratic blocks. I have 

 endeavoured to indicate on the map the highest points on which the 

 erratic rocks are found, and to ascertain the heights by direct baro- 

 metric observations. 



In the lower parts of these mountains, below 4000 and 3500 feet, 

 the erratic rocks are seen everywhere scattered about in more or less 

 abundance. 



I may be allowed to mention some points which seem to me of 

 importance for forming an estimate of the way in which these remark- 

 able erratic rocks have been transported. 



The erratic pebbles in the mountain chains under consideration 

 generally reach an elevation of 4000 and 4400 Fr. feet, in some 

 cases even 4600 ! Even on these highest limits we generally find 

 rounded pebbles of 5 to 20 centimetres chameter. Hornblende rocks, 

 with manj massive and schistose varieties, are prevalent ; there are 

 also found mica-schist and gneiss, as well as some fragments of 

 granite. 



Even on the isolated summit of the Peissenberg, nine English miles 

 distant from the Alps, at an elevation of 3005 Fr. ft., thick layers 

 of dilmdal boulders occur, with rolled erratic rocks. Further it is 

 to be remarked, that the erratic rocks are not only deposited on the 

 surface of the older diluvial boulder beds, but that they are also 

 disseminated in their interior, and that they are found in their very 

 lowest beds, down to the surface of the miocene tertiary deposits. 



The deep valleys which have been cut through the thick boulder 

 beds of the Bavarian plateau by the greater rivers, for instance by 

 the Tsar, afford very excellent opportunities for the study of these 

 phsenomena. In the Yalle}'^ of the Tsar, in the environs of ^Munich, 

 the erratic pebbles in the lower beds are all rounded, and do not 

 generally exceed the size of the fist. Erratic blocks of very considerable 

 dimensions are not very common on the plateau around the Tsar and 



