John Ball — Soundings in the Lake of Como. 359 



EXPLANATION OF PLATE IX. 



Fig. \a, h. Upper and under side of Plactmopsis Jurensis, Morris and Lycett. Corn- 

 brash, Scarborough. 



Fig. 2. Flacunopsis, sp. nov. Inferior Oolite, near Stroud. 



Fig. 3«, b. Upper and under side of Ostrea, sp. Cornbrash, Weymouth. 



Fig. 4. Ideal section of Ostrea, showing growth (see page 357). 



Fig. 5a, b, c. Upper and under side, and section of Ostrea, which has grown on the 

 back of Ammonites Serveyi. Cornbrash, Peterborough. 



III. — Notice of Soundings executed in the Lake of Como, with 

 A view to determine the Foem of its Bed. 



By John Ball, F.E.S. 



(PLATE X.) 



THOSE who have taken part in the recent discussions as to the 

 origin of lake -basins are well aware that one of the chief 

 causes which has retarded a settlement of the controversy is the 

 ignorance prevailing as to the true form of such basins. Even as to 

 the Swiss and Lombard lakes, constantly visited as they have been 

 by men of science, the data are extremely scanty and no way 

 reliable. A few soundings made by myself in the Lake of Como, 

 in 1863, and referred to in a paper published in the Philosophical 

 Magazine in the following December, increased my conviction of the 

 importance of instituting careful and exact measurements of the 

 form and dimensions of the beds of lakes, if we were to reason 

 securely as to their origin. I expressed that conviction at the time 

 to an active local naturalist, Don Baldassare Bernasconi, residing at 

 Laglio. In 1865 Signer Gentilli, one of the engineers of the 

 Lombardo-Venetian Railway, being for some months on the Lake, 

 proposed to undertake a regular survey of the bed of the Lake by 

 means of a complete series of soundings, and devised an instrument 

 for measuring the distances traversed horizontally in a boat, corre- 

 sponding to each cast of the sounding line. Signor Gentilli found 

 two active coadjutors in the persons of the above-named ecclesiastic, 

 and of Dr. Guiseppe Casella, also resident at Laglio, on the Lake. 



The results were published by Signor Gentilli in a paper inserted 

 in the second volume of the Memoirs of the " Societa Italiana di 

 Scienze Naturali," and also in a little tract, entitled "Cenni 

 Orografici sul Lago di Como," by MM. Casella and Bernasconi, 

 both dated in 1866. 



It is apparent that the authors of the second paper found cause for 

 complaint as to the form adopted by Signor Gentilli for the publica- 

 tion of results which had been mainly obtained through the labour 

 and perseverance of his coadjutors. 



An examination of the plans and sections contained in both papers 

 displays a general agreement in the results, showing that they are 

 derived from identical materials, along with some discrepancies easily 

 accounted for when we recollect that some of the sections ai-e 

 executed independently, and do not follow the same line exactly. 



