A b s t r ac t . We study the fan structure of Dressians Dr (d, n) and local Dressians Dr(M) for a given matroid M. In particular we show that the fan structure on Dr(M) given by the three term Plücker relations coincides with the structure as a subfan of the secondary fan of the matroid polytope P (M). As a corollary, we have that a matroid subdivision is determined by its 3-dimensional skeleton. We also prove that the Dressian of the sum of two matroids is isomorphic to the product of the Dressians of the matroids. Finally we focus on indecomposable matroids. We show that binary matroids are indecomposable, and we provide a non-binary indecomposable matroid as a counterexample for the converse. arXiv:1809.08965v1 [math.CO] 24 Sep 2018 Cambridge University Press, Cambridge, 1986.I n s t i t u t f ü r M at h e m at i k , F U B e r l i n , A r n i m a l l e e 2 , 1 4 1 9 5 B e r l i n , G e r m a n y , E -m a i l : o l a rt e @ z e dat . f u -b e r l i n . d e I n s t i t u t f ü r M at h e m at i k , T U B e r l i n , S t r . d e s 1 7 . J u n i 1 3 6 , 1 0 6 2 3 B e r l i n , G e r m a n y , E -m a i l : pa n i z z u t @ m at h . t u -b e r l i n . d e D e pa rt m e n t o f M at h e m at i c a l S c i e n c e s , B i n g h a m t o n U n i v e r s i t y , B i n g h a m t o n , N Y 1 3 9 0 2 , U S A , E -m a i l : s c h ro e t e r @ m at h . b i n g h a m t o n . e d u