28 



SCIENCE PROGRESS. 



been self-supporting, but must have rested on older sedi- 

 ments the gap below it must have been filled up with a 

 succession of horizontal deposits as shown in Fig. 3. This 

 state of things again was not original, there was a time 

 when these sediments did not exist, and the Tuscan district 



appeared as in Fig. 4. Once more, the argument which 

 applied to the latest rocks, holds equally for the older ones 

 G, F, so that we must restore these, first as represented in 

 Fig. 5, and next as in Fig. 6. Beyond the last stage, when 

 Tuscany lay inchoate, a mass of sediments beneath a prim- 

 aeval sea, we can only take one step farther back into the 



